Ontario Defendant's Claim and Counterclaim Estimator
Arithmetic comparison only - not a predicted judgment
- Defendant's Claim filing fee
- $108.00
- Jurisdiction check on defendant's claim (limit $50,000)
- under
Arithmetic comparison only - not a predicted judgment. The two claims are legally distinct, and there is no automatic netting between them. A judge decides liability and judgment separately on each side.
A Defendant's Claim may be brought against the plaintiff, a co-defendant, or another person where the Rules permit. Party joinder, jurisdiction, service and relatedness of the claims all require legal analysis.
About this calculator
In the Small Claims Court a defendant who wishes to make a claim of their own files a Defendant's Claim (Form 10A) - the equivalent of what many lawyers colloquially call a counterclaim, though the Rules use the "Defendant's Claim" terminology. Rule 10.01 requires a Defendant's Claim to be issued within 20 days after the Defence is filed, unless the court orders otherwise.
The $50,000 monetary jurisdiction applies to the defendant's own claim just as it does to the plaintiff's claim, excluding interest and costs. If the defendant's proposed claim exceeds $50,000, options include abandoning the excess or pursuing the claim in the Superior Court of Justice.
Worked example
Facts. A plaintiff claims $12,000. The defendant proposes a Defendant's Claim of $4,500 arising out of the same dealings.
Arithmetic comparison only - not a predicted judgment. $12,000 - $4,500 = $7,500. That $7,500 is a mathematical difference between two proposed figures, nothing more.
What can actually happen. Either claim may be dismissed in full. The court may allow the plaintiff $9,000 and the defendant nothing, or allow the defendant $4,500 and the plaintiff $2,000, or reach any other combination the evidence supports. The two claims are decided on their own merits, so a $7,500 difference is not a forecast of what anyone will be ordered to pay.
On the same facts, the defendant would also pay the $108 filing fee to issue the Defendant's Claim, and the plaintiff would then have 20 days after service to file a Defence to it.
How this calculation works
This page does two separate things and keeps them apart. It subtracts the proposed Defendant's Claim from the Plaintiff's Claim to show the mathematical difference, and it applies the Rules to the dates you enter to estimate the procedural deadlines.
The subtraction is arithmetic comparison only - not a predicted judgment. There is no automatic netting between a Plaintiff's Claim and a Defendant's Claim. They remain legally separate proceedings within the same action, each of which must be proved. The tool also checks the proposed Defendant's Claim against the monetary jurisdiction in the same way it would check any claim.
| Step | What the Rules and fee schedule provide |
|---|---|
| Form | A Defendant's Claim is made in Form 10A. |
| Who may be claimed against | The plaintiff, a co-defendant, or another person, in the circumstances Rule 10.01 permits. |
| Ordinary time to issue | Within 20 days after the Defence is filed. |
| Issuing later | A Defendant's Claim may be issued later, before trial or the assessment of damages on a default judgment, only with leave of the court. Leave is not automatic. |
| Where it is issued | In the same court office as the Plaintiff's Claim. |
| Filing fee | $108.00 to issue a Defendant's Claim, under the current fee schedule. |
| Service | The issued Defendant's Claim must be served within six months. |
| Defence to a Defendant's Claim | Filed within 20 days after service of the Defendant's Claim, under Rule 10.03. |
| How it is heard | A Defendant's Claim is ordinarily tried together with the main action, unless the court orders otherwise. |
Why a Defendant's Claim rather than a set-off
A defendant who only pleads a reduction in the Defence is limited to defending. A Defendant's Claim is usually the better route where the defendant wants a judgment of their own, because it can also bring in another person where Rule 10.01 permits, rather than being confined to the parties the plaintiff chose to sue.
That advantage comes with obligations: a separate claim to prove, a filing fee, service within six months, and exposure to a Defence and to costs on that claim.
What the tool includes
- A side-by-side comparison of the Plaintiff's Claim and the proposed Defendant's Claim, with the difference labelled as arithmetic only.
- An estimated ordinary issuing deadline measured from the date the Defence was filed, with weekend and holiday rolling applied.
- A jurisdiction check on the proposed Defendant's Claim against the monetary limit.
- The current filing fee to issue a Defendant's Claim.
- A reminder of the Rule 10.03 window for a Defence to the Defendant's Claim.
What it does not decide
- Whether the proposed claim is sufficiently connected to the main action, or whether the Rules permit it against the person you have in mind.
- Whether you have a cause of action at all, or what it is worth.
- Whether a limitation period has expired for the defendant's own claim.
- Whether the Small Claims Court is the right court for the claim, or the right location.
- How the parties should be named, or whether the correct legal entities have been identified.
- Whether service was valid, or when service is effective for counting the Rule 10.03 window.
- Whether the court will grant leave for a Defendant's Claim issued outside the ordinary window.
- What any judgment will be. The difference figure is a comparison of two proposed amounts, not a result.
If no Defence to a Defendant's Claim is filed, the consequence is not a clerk-signed judgment appearing automatically. The official guide describes judgment on a Defendant's Claim being obtained at trial or on a motion, so plan on having to take a further step and prove the claim.
Common mistakes
- Reading the difference as the amount someone will be ordered to pay. It is arithmetic comparison only - not a predicted judgment.
- Assuming the two claims cancel out. There is no automatic netting; each claim must be proved.
- Counting the 20 days from service of the Plaintiff's Claim rather than from the filing of the Defence.
- Assuming a late Defendant's Claim can simply be issued. Outside the ordinary window it takes leave, and leave is not automatic.
- Issuing in a different court office from the Plaintiff's Claim.
- Issuing the claim and then letting the six-month service window lapse.
- Forgetting that a Defence to the Defendant's Claim is due 20 days after that claim is served, which is a deadline for whoever is claimed against.
- Treating a Defendant's Claim as a costs-free tactic. It carries a filing fee and its own costs exposure.
- Assuming a default on the Defendant's Claim converts into judgment without a further step.
Before relying on the result
- Confirm the date the Defence was actually filed with the court office, not the date it was served or received.
- Check the current text of Rules 10.01 and 10.03 before you rely on any deadline shown here.
- Confirm the current filing fee with the court office or the fee schedule before you attend.
- Diarise both the issuing deadline and the six-month service deadline as soon as you decide to proceed.
- Get legal advice on the connection between the claims, on limitation periods, and before naming anyone who is not already a party.
- Plan how you would prove the claim at trial, since that is where a Defendant's Claim is ordinarily decided.
Three worked examples
Fictional teaching examples - not legal authority. Each shows the arithmetic and the deadlines the tool produces, and stops before every question that is legal rather than arithmetic.
Example 1 - an ordinary counterclaim inside the window. The defendant is sued for $9,000 for unpaid renovation work and files the Defence on 5 March 2026. The Defendant's Claim for $4,000 in deficiency costs is issued against the same plaintiff. The 20-day issuing period runs from the Defence filing date, and the claim must then be served within six months of issuance. The two figures do not net off: the plaintiff still has to prove $9,000 and the defendant still has to prove $4,000.
Example 2 - a claim larger than the plaintiff's. The plaintiff claims $7,500 and the defendant's own claim is $18,000. The arithmetic difference is $10,500 in the defendant's favour, but that is a comparison of pleaded amounts, not a predicted outcome. The Defendant's Claim itself must stay within the court's monetary jurisdiction, it attracts its own filing fee, and whoever is claimed against has 20 days after service to defend it.
Example 3 - past the ordinary window, and a new party. The Defence was filed months earlier and the defendant now wants to bring in a subcontractor who is not yet a party. Outside the ordinary 20-day period a Defendant's Claim may be issued only with leave, which must be obtained before trial or before default judgment, and leave is not automatic. Whether the subcontractor can properly be named, and whether the claim is sufficiently connected to the Plaintiff's Claim, is a legal question this page does not decide.
Practical next steps
- Confirm the Defence filing date from the court file before diarising anything.
- Diarise the issuing deadline and the separate six-month service deadline together.
- Read the ministry Replying to a claim guidance and the current Form 10A before drafting.
- Confirm the current filing fee with the court office.
- Get legal advice on connection to the Plaintiff's Claim, on limitation periods, and before naming a person who is not already a party.
Official sources checked for this page: O. Reg. 258/98 (Rules 10.01 and 10.03), the ministry's Guide to Procedures in Small Claims Court - Replying to a claim and Form 10A, Defendant's Claim. Reviewed on 21 August 2026. The worked examples and the next-step checklist were added at that review; the deadline engine and the fee figures were unchanged.
Legal information reviewed: 31 July 2026. Checked against the official sources listed on this page. Rates, fees and rules change; confirm anything you rely on.
Frequently asked questions
Is "counterclaim" the right word?
What if we're past the 20 days?
Can the defendant sue a third party?
Related calculator and guides
- Defendant's Claim in the Ontario Small Claims Court
Who may be claimed against under Rule 10.01(1), the 20-day issuing window, and the Rule 10.03 defence deadline.
- Small Claims Court jurisdiction and how to size a claim
The $50,000 limit applies to a Defendant's Claim in the same way.
Official sources
- Rules of the Small Claims Court, O. Reg. 258/98 - Rules 3.01, 10.01
- Guide to Procedures in the Small Claims Court - Making a claim
- Guide to Procedures in the Small Claims Court - Serving documents
- O. Reg. 332/16 - Small Claims Court fees
- Courts of Justice Act
- Guide to Procedures in Small Claims Court