Sued, but they owe
you too? Countersue.

By Jonathan Kleiman, Barrister & Solicitor · Published June 2026

One of the most common reactions I hear when someone gets served with a Small Claims Court claim is not fear — it is frustration. "They are suing me? They are the ones who owe me money." If that is where your head is at, you are in exactly the position that rule 10 of the Rules of the Small Claims Court was written for. You do not have to sit there and only defend. You can sue back.

The tool for doing it is called a Defendant\'s Claim, filed on Form 10A. It is Small Claims Court\'s all-in-one version of what lawyers in the higher courts would call a counterclaim, a crossclaim, or a third-party claim. With one document you can claim against the person who sued you, against someone sued alongside you, or against a brand-new party you say is really responsible for the mess. And crucially, it gets heard together with the original claim, in the same case, on the same day.

But there is a catch that catches people constantly: timing. A Defendant\'s Claim has to be issued within a tight window tied to your Defence, and if you blow your Defence deadline you can lose the main case before your counterclaim ever gets off the ground. Below I will walk through what the Defendant\'s Claim is, who you can use it against, the deadlines that actually matter, and the strategy — because a good counterclaim is not just a defence. It can flip the whole dispute.

Understanding the question: yes, you can countersue

Let me answer the headline directly, because people are often surprised it is even possible. Yes — in Ontario Small Claims Court you can countersue, and the mechanism is the Defendant\'s Claim under rule 10. You do not start a separate lawsuit, pay a separate set of court dates, and hope the two cases somehow line up. Your claim is folded into the file that was already opened against you.

Think of it this way. When you are served, the court has already created a case with a number. The Defendant\'s Claim lets you add your own claim to that existing case rather than opening a new one. The same deputy judge hears both. The settlement conference covers both. The trial, if it gets there, deals with both at once. That efficiency is the whole point — Small Claims Court would rather resolve a dispute completely in one proceeding than have related claims bouncing around in separate files.

So if your instinct is "they owe me too," the law agrees that the place to raise it is right here, in this case, with a Form 10A. The question is not really whether you can — it is whether you do it on time and whether your claim is strong enough to be worth bringing.

Is a Defendant\'s Claim the same as a counterclaim?

Essentially, yes — with a twist. In the Superior Court, a counterclaim, a crossclaim, and a third-party claim are three different documents for three different targets. Small Claims Court rolls all three into the single Defendant\'s Claim. So when people ask me if they can "file a counterclaim" in Small Claims, the answer is that the counterclaim is a Defendant\'s Claim — it is just that the same form also covers situations a counterclaim alone would not.

From my experience

From my experience, the cases where a Defendant\'s Claim matters most are the ones where the plaintiff has picked the order of events to their advantage. A contractor and a homeowner fall out near the end of a job. The homeowner refuses to pay the final invoice and sues the contractor for a botched detail. From the homeowner\'s side, the story is "your work was defective." From the contractor\'s side, the story is "you never paid me $9,000." Both can be true. Whoever sues first frames the case — but the Defendant\'s Claim lets the other side put their half of the story on the record as a live claim, not just a defence.

I have seen what happens when a defendant only defends and does not counterclaim. They win the point that they do not owe the plaintiff anything — and then they are left having to start a whole new lawsuit to recover what they are owed, months later, after the dust has settled. That is two cases, two filing fees, two sets of court dates, for what could have been one. The Defendant\'s Claim avoids all of that, provided you raise it inside the window.

The other thing experience has taught me is psychological. A plaintiff who served a claim expecting an easy win reacts very differently once they receive a Defendant\'s Claim of their own. Suddenly they are exposed too. In a meaningful share of those files, the conversation shifts from "pay us" to "how do we make this all go away" almost overnight. That shift is worth understanding before you decide how to respond to being sued.

What the law generally says

The rules around the Defendant\'s Claim are not complicated, but the details are where people slip. Here is what actually governs it.

• The form and the rule. A Defendant\'s Claim is made on Form 10A under rule 10 of the Rules of the Small Claims Court. It is issued by the court, just like a Plaintiff\'s Claim, and becomes part of the existing case.
• Who you can claim against. Rule 10 lets you claim against the plaintiff (a counterclaim), against a co-defendant sued alongside you (a crossclaim), and/or against a new third party who is not yet in the case but who you say is responsible for all or part of the plaintiff\'s claim (a third-party claim). One form, three possible targets.
• The 20-day timing. This is the one to burn into your memory. A Defendant\'s Claim must be issued within 20 days after you file your Defence, unless the court grants leave to file it late. So you file your Defence on time first, then issue the Defendant\'s Claim within 20 days of that Defence.
• Serving it. Once your Defendant\'s Claim is issued, it must be served within six months. A party who is on the receiving end of a Defendant\'s Claim then files their own Defence (Form 9A) within 20 days of being served — the same flat window that applied to you on the original claim.
• The fee. Issuing a Defendant\'s Claim carries a filing fee, similar to the fee for a Plaintiff\'s Claim. It is your own claim, so the court charges for it.
• The limits. Your claim has to fit within the $50,000 Small Claims limit and within the two-year limitation period under the Limitations Act, 2002, and it should be connected to the dispute or against someone responsible for it.

Notice how the deadlines stack. You get 20 days from service to defend, and then 20 days from filing your Defence to issue the Defendant\'s Claim. People who only watch the first deadline often forget the second one is already running. The cleanest approach, and the one I usually recommend, is to prepare your Defence and your Defendant\'s Claim together and file them at the same time.

Common situations I see

Over the years, the same fact patterns keep coming back, and each one shows the Defendant\'s Claim doing a slightly different job.

The contractor sued for an unpaid balance. A trade is sued by a customer who withheld the final payment, claiming the work was defective. The contractor counters with a Defendant\'s Claim for the unpaid balance — say the customer is suing for $6,000 to fix the work, and the contractor counters for the $9,000 invoice that was never paid. Now both numbers are in front of the same judge, and the case is really about the net difference. This is the single most common counterclaim I see, and it usually turns on whether there was a breach of contract on either side.

Bringing in a third party who is really responsible. A defendant is sued for something that was actually caused by someone not yet in the case. The homeowner sues the general contractor; the general contractor brings in the subcontractor whose plumbing failed. Or a retailer is sued over a defective product and brings in the manufacturer or distributor that supplied it. The third-party claim pulls the real source of the problem into the existing case so liability gets sorted out once, not in a chain of separate lawsuits.

The customer sued who counters for defective goods. The flip side of the first example. A buyer is sued for not paying for goods or services and responds that what they received was defective, late, or never delivered as promised. Rather than just defending "I should not have to pay," they bring a Defendant\'s Claim for their own losses — the cost of fixing or replacing the defective goods, or money already paid for something that did not work. That converts a defensive posture into an affirmative claim with its own value.

Step-by-step: how to countersue

The mechanics are straightforward once you see them laid out in order. The trap is almost always the sequence and the timing, not the paperwork itself.

1. File your Defence first, within 20 days

When you are served with the Plaintiff\'s Claim, your first job is to file a Defence (Form 9A) within the flat 20-day window. This protects you on the main case so you cannot be noted in default while you are busy thinking about countersuing. If you are not sure when your deadline falls, run the dates through the Ontario Small Claims Court defence deadline calculator. The full picture of being on the receiving end is in my guide on what to do when someone is suing you in Small Claims Court.

2. Issue the Defendant\'s Claim within 20 days of the Defence

Once your Defence is filed, the clock for your Defendant\'s Claim starts: you have 20 days from that Defence to issue the Form 10A. In practice I prepare both documents together and file them at the same time, which removes the risk of forgetting the second deadline entirely. The Defendant\'s Claim is issued by the court and given the same case number as the original claim.

3. Serve the Defendant\'s Claim

A claim that is issued but not served does nothing. Once issued, you have six months to serve your Defendant\'s Claim on whomever you are claiming against — the plaintiff, a co-defendant, or a new third party. As with any claim, serve promptly; sitting on it only delays the case you are now driving. The mechanics of issuing and serving mirror the process I describe in how to sue in Small Claims Court in Ontario.

4. They defend within 20 days

The party you have served with the Defendant\'s Claim now stands in your old shoes. They have a flat 20 days from being served to file their own Defence (Form 9A) to your claim. If they do not, you may be able to note them in default on the Defendant\'s Claim, the same way a plaintiff would. From here the combined case proceeds through the usual stages — settlement conference first, then trial if it does not resolve.

Important things to know

A few features of the Defendant\'s Claim matter enough that I raise them with every client who is weighing whether to bring one.

Your own claim has to fit the box. A Defendant\'s Claim is a real claim, so it lives by the same constraints as any other Small Claims action. It must be within the $50,000 limit and within the two-year limitation period. If your claim against the plaintiff is itself out of time, the fact that they sued you first does not revive it. Check where you stand with the limitation period calculator before you assume you can bring it.

It should be connected. Rule 10 contemplates claims that are tied to the dispute or against a party responsible for it. A counterclaim that arises from the same transaction — the same contract, the same job, the same deal gone wrong — is exactly what the rule is built for. Trying to bolt on an entirely unrelated grievance against the plaintiff is a harder fit and can draw objections.

A frivolous counterclaim carries a costs risk. This is the warning I give most often. A genuine counterclaim is leverage. A counterclaim with no real basis, brought to harass or to muddy the water, is the opposite — it can irritate the deputy judge and expose you to a costs award if it fails. The strength of the underlying claim is what gives a Defendant\'s Claim its power, not the mere fact of filing one.

Common mistakes

The errors I see around countersuing are almost always about timing and temperament rather than law. A few come up over and over.

Missing the Defence deadline and getting defaulted. This is the worst one. People get so focused on the idea of suing back that they let the 20-day Defence window pass. If you are noted in default on the main claim, you can lose that case outright — and your grand plan to countersue is now happening from a hole you dug yourself. Defend on time, always. The counterclaim is the second move, not the first.

Sitting on the counterclaim past 20 days. Even people who file their Defence promptly sometimes treat the Defendant\'s Claim as something they can get to "whenever." But the 20-day clock from your Defence is real. Let it lapse and you are reduced to asking the court for leave to file late, which it may or may not grant. Do not put yourself at the mercy of that discretion when filing on time was entirely within your control.

Counter-suing out of spite. Being sued is irritating, and the urge to hit back is natural. But a Defendant\'s Claim should be a claim you would have been willing to bring on its own merits, not a reflex. A retaliatory counterclaim with no substance wastes your filing fee, drags out the case, and can land you with a costs order. Ask yourself honestly whether you would sue this person if they had never sued you. If the answer is no, think hard before filing.

What happens in court

Once a Defendant\'s Claim is in the file, the two claims travel together. There is not a separate hearing for the main claim and another for the counterclaim — the settlement conference and, if needed, the trial deal with both at the same time, in front of the same deputy judge.

At trial, the judge effectively keeps two ledgers. They decide whether the plaintiff proved their claim against you, and separately whether you proved your Defendant\'s Claim. Then they net the two. If the plaintiff wins $6,000 and you win $9,000 on your counterclaim, the practical result is a judgment in your favour for the $3,000 difference, plus whatever the judge orders on interest and costs. The party who started as the defendant can walk out as the net winner — which is exactly the outcome a good counterclaim is built to produce.

This netting is also why the Defendant\'s Claim is so much more powerful than simply defending. A successful defence gets you to zero. A successful Defendant\'s Claim can take you past zero into positive territory, with the court ordering the original plaintiff to pay you.

Settlement considerations

A counterclaim changes the leverage, and that is often its biggest value — more than what happens at trial, because most cases never get that far. When you are only defending, the entire downside risk in the negotiation sits on your side: the worst case is you pay, the best case is you pay nothing. With a live Defendant\'s Claim, the plaintiff now has their own downside. They could lose and have to pay you.

That two-sided exposure is what makes settlements happen. At the settlement conference, a deputy judge looking at claims running in both directions will often nudge the parties toward a number in the middle, or toward simply walking away with mutual releases. I have settled plenty of files where the existence of a credible counterclaim was the only reason the plaintiff came to the table at all.

The flip side, again, is that this only works when the counterclaim is genuine. A deputy judge sees a lot of cases and can usually tell the difference between a real claim and a tactical one within minutes. Real leverage comes from a claim you could win, not from the noise of having filed something.

Key takeaways

• You can countersue with a Defendant\'s Claim. Form 10A under rule 10 is Small Claims Court\'s version of a counterclaim, crossclaim, and third-party claim rolled into one — heard together with the main case.
• Defend first, then countersue. File your Defence within the flat 20 days from service, then issue the Defendant\'s Claim within 20 days of that Defence. The safest move is to file both together.
• You can claim against three kinds of party. The plaintiff who sued you, a co-defendant sued alongside you, or a new third party you say is really responsible.
• The same limits apply. Your claim must fit the $50,000 ceiling and the two-year limitation period, carry its filing fee, and be connected to the dispute.
• A genuine counterclaim changes the leverage. It can offset or exceed what you allegedly owe and pull the plaintiff to the table — but a frivolous one risks a costs award.

Frequently asked questions

Can I sue someone back in Small Claims Court?

Yes. If you have been served with a Plaintiff's Claim and the plaintiff actually owes you, you can sue them back in the same case using a Defendant's Claim (Form 10A) under rule 10 of the Rules of the Small Claims Court. This is Small Claims Court's version of a counterclaim. You do not have to start a separate lawsuit — your claim is folded into the existing file and heard at the same time. The key is timing: file your Defence first, then issue the Defendant's Claim within 20 days of filing that Defence.

What is a Defendant's Claim?

A Defendant's Claim (Form 10A) is the document a defendant uses under rule 10 to make their own claim inside a case that has already been started against them. It is the Small Claims Court's combined version of a counterclaim, a crossclaim, and a third-party claim. With it you can claim against the plaintiff who sued you, against a co-defendant who was sued alongside you, or against a brand-new third party you say is really responsible for all or part of the plaintiff's claim. It is issued by the court, given a fee, and heard together with the main claim.

How long do I have to file a Defendant's Claim?

A Defendant's Claim must be issued within 20 days after you file your Defence, unless the court grants leave to file it late. So the sequence matters: you have 20 days from service to file your Defence (Form 9A), and then a further 20 days from that Defence to issue the Defendant's Claim. Once it is issued, you have six months to serve it. If you miss the 20-day window, you are not automatically out of luck, but you have to ask the court's permission, which is never guaranteed. The safest move is to file both together.

Do I have to file a Defence too?

In almost every case, yes. A Defendant's Claim is built on top of your Defence, not in place of it. You have a flat 20 days from service to file your Defence (Form 9A) to the plaintiff's claim, and the 20-day window to issue your Defendant's Claim runs from that Defence. If you skip the Defence and only think about countersuing, you risk being noted in default on the main claim — meaning you could lose the case against you even while you are trying to bring your own. Defend first, countersue second.

Can I bring in a third party who is really responsible?

Yes, and this is one of the most useful features of rule 10. If you are sued but someone who is not yet in the case is actually responsible for all or part of the claim, you can bring them in with a Defendant's Claim as a third-party claim. A classic example is a contractor sued by a homeowner who points to a subcontractor whose bad work caused the problem. Instead of paying and then chasing the subcontractor in a separate lawsuit, you pull them into the existing case so liability gets sorted out in one proceeding.

Is there a fee to countersue?

Yes. Issuing a Defendant's Claim carries a filing fee, similar to the fee for issuing a Plaintiff's Claim. It is not free just because the case already exists — you are starting your own claim within it, and the court charges accordingly. The exact amount depends on whether you are a frequent or infrequent claimant, but you should budget for it. If you win your Defendant's Claim, that fee and other allowable costs can often be recovered. I always factor the fee into the bigger question of whether the counterclaim is worth bringing in the first place.

Can I counterclaim for more than the original claim?

Yes. There is no rule that your Defendant's Claim has to be smaller than, or even related in size to, the plaintiff's claim. If they sued you for $8,000 and you genuinely believe they owe you $30,000, you can claim the full $30,000 — provided it stays within the $50,000 Small Claims limit and the two-year limitation period. This is exactly why a counterclaim can flip the dynamics of a case. A defendant who was on the back foot suddenly becomes the party owed more money, which changes both the leverage and the settlement conversation considerably.

What if my counterclaim is over $50,000?

Small Claims Court can only deal with claims up to $50,000, not counting interest and costs, so a Defendant's Claim has to respect that same ceiling. If your claim is genuinely worth more, you have a decision to make. You can abandon the portion over $50,000 and claim the rest in Small Claims, which keeps everything in one simple forum. Or, if the excess is significant, you may need to look at the Superior Court, which can create real complications when the main claim is already in Small Claims. This is a situation where I would want to map out the strategy carefully before filing anything.

Does counter-suing change my chances of settling?

Often, yes — and usually in your favour, if the counterclaim is genuine. A plaintiff who filed expecting a straightforward win now faces their own exposure, which is a powerful motivator to talk. A solid Defendant's Claim can offset or even exceed what you allegedly owe, turning a one-way demand into a two-way negotiation. The caution is that this only works when the counterclaim is real. A counterclaim filed out of spite, with no genuine basis, tends to annoy the judge and can expose you to a costs award. Leverage comes from a legitimate claim, not a retaliatory one.

Do I need a lawyer or paralegal to countersue?

You are allowed to file a Defendant's Claim yourself — Small Claims Court is designed to be accessible to self-represented people, and many do it well. That said, a counterclaim adds moving parts: a deadline stacked on a deadline, the question of who to claim against, and the strategy of how it interacts with the main case. Where I see self-represented defendants get into trouble is missing the Defence deadline or filing a weak counterclaim that backfires on costs. If the numbers are meaningful or a third party is involved, it is often worth at least a consultation to get the structure right before you file.

Final thoughts

Being served with a Small Claims Court claim is not the end of the conversation — sometimes it is only the opening move. If the person suing you genuinely owes you money, or if someone else is really to blame, the Defendant\'s Claim under rule 10 lets you put that on the record inside the same case rather than starting over later. Done right, it can turn a case you were defending into a case you are winning.

The discipline that makes it work is timing. Defend within your 20 days, issue your Defendant\'s Claim within 20 days of that Defence, and serve it promptly. Get the sequence right and you keep all your options open. Get it wrong and you can find yourself defaulted on the main claim or shut out of the counterclaim you were entitled to bring. If a third party is involved or the numbers are meaningful, it is worth getting the structure right the first time — the cost of doing it twice is almost always higher.

If you have been served and you think they owe you too, talk it through before the clock runs. Call a Small Claims Court defence lawyer or a Toronto Small Claims Court lawyer at 416-554-1639, or book a free consultation. A short conversation can usually tell you whether a counterclaim is worth bringing — and make sure you do not miss the deadline while you decide.