When damages are demanded without evidence: what it costs to be wrong
A letter that states a damages figure without invoices, licence comparables or an expert calculation is not evidence of loss. It is an opening position, nothing more. Treating it as proven — paying or conceding before it is tested — is usually the costlier mistake. Ignoring it entirely is the second-costliest one, because a response window and a separate limitation clock are both already running. The correct move is procedural: challenge the quantum in writing, preserve your own records, and reply within the stated period.
What actually governs the claim
Patent damages claims sit under different procedural regimes depending on which patent is in dispute. A European patent with unitary effect, or a classical European patent for which no opt-out was filed during the transitional period, falls under the Agreement on a Unified Patent Court. A national patent, and an opted-out European patent, stays with the national court that has jurisdiction over the defendant or over the place of the alleged infringement. Which forum applies changes the timetable, the disclosure rules and, in practice, how quickly an unsubstantiated figure gets tested.
The framework around unitary patent protection sits in three instruments:
| Instrument | Reference | In force from | What it covers |
|---|---|---|---|
| Regulation | Regulation (EU) No 1257/2012 | 2023-06-01 | Unitary effect of a European patent across participating states |
| Regulation | Council Regulation (EU) No 1260/2012 | 2023-06-01 | Translation arrangements applicable to the unitary patent |
| Agreement | Agreement on a Unified Patent Court | 2023-06-01 | Court with jurisdiction over infringement and damages claims for unitary and non-opted-out European patents |
None of these three instruments sets the standard of proof for a damages figure itself. That standard is procedural and belongs to whichever forum actually hears the case — the Unified Patent Court's own rules of procedure, or the applicable national code of civil procedure, depending on which one applies to the patent in question.
What changes once the letter arrives
A demand without substantiation shifts nothing on its own. The burden of proving loss, or of proving a reasonable royalty as an alternative measure, stays with the claimant throughout. What does change is the clock. Most procedures attach a response window to a formal demand, and a separate, longer limitation period on the underlying claim keeps running regardless of whether you reply. Silence stops neither clock. In some venues, a late or absent reply can even be read as an admission by conduct, quite apart from whether the quantum itself was ever tested.
What to do, in order
- Ask, in writing, for the basis of the figure — invoices, licence comparables or an expert report — before addressing the merits of infringement at all.
- Record the date the letter was served. It usually starts the reply clock and marks the point from which a limitation defence, if you need one, is measured.
- Instruct patent counsel to draft a reply that disputes the quantum without conceding the underlying infringement allegation.
- Establish which patent, which claims and which forum are actually at stake before committing to any procedural strategy.
- Gather your own records of use, sales and development cost now, while they are easy to reconstruct — they become your evidence if the matter proceeds.
- Do not pay or settle before the quantum has been tested by a court or a neutral expert. An early payment is hard to characterise later as anything other than an admission.
Ownership of the underlying technical file matters as much as the figure in the letter. If design or engineering records sit with a third party rather than with you, that gap has to close before your own evidence can be assembled — the position is close to the one described in When an agency keeps the design files explained.
Who decides, and on what
The forum decides on the evidence the parties file, not on the figure stated in the initial letter. For a claim under the Agreement on a Unified Patent Court, the court applies its own rules on disclosure and quantum. For a claim before a national court, the applicable civil procedure code governs disclosure, expert evidence, and the standard the claimant must meet to succeed. In both settings, an unsubstantiated figure carries no weight until the claimant files supporting material: invoices, comparable licences, or an expert calculation of lost profit or a reasonable royalty.
Comparable licences are often the weakest part of a demand letter, because a royalty rate that looks plausible on paper still has to be tied to an actual transaction between real parties. Where royalty income itself is disputed on separate grounds — for instance because it is tracked on a distributed ledger rather than through conventional invoicing — the evidentiary problem is structurally similar; see When royalties encoded on-chain are ignored and its limits.
Three scenarios
If the patent is a national patent, the national court decides under national procedural law, and the Agreement on a Unified Patent Court has no application at all.
If the patent is a European patent with unitary effect, or a classical European patent that was not opted out during the transitional window, the Unified Patent Court has jurisdiction, and its own evidentiary rules apply from the first procedural step.
If the claimant has not yet identified which patent, which claims and which product are actually said to be infringed, the letter is closer to a pressure tactic than a filed claim. The priority is to request that identification in writing before any substantive reply.
What this page does not cover
This page does not calculate what a specific claim is worth, and it does not replace representation once proceedings are filed. It does not cover criminal counterfeiting remedies or customs seizure procedures, which sit under separate instruments entirely. Before a dispute reaches this stage, checking who is actually behind the counterparty making the demand is a cheaper step than defending the claim itself; see Counterparty report before appointing a developer explained.
Verified
Checked against the sources listed below at the time of publication. Instruments cited: Regulation (EU) No 1257/2012, Council Regulation (EU) No 1260/2012, Agreement on a Unified Patent Court. Correspondence or file material you send us in connection with a damages dispute is handled under the two bases described in the Privacy notice: two roles, two bases and the deadline.
Frequently asked questions
What is the first step when damages are demanded without evidence?
Ask in writing for the basis of the figure — invoices, licence comparables or an expert calculation — before responding to the substance of the infringement claim.
Which deadline is already running?
Usually two: a short response window tied to the letter itself, and a separate, longer limitation period on the underlying claim, which keeps running whether or not you reply.
Who decides, and on what evidence?
The court with jurisdiction over the patent decides — the Unified Patent Court for a unitary or non-opted-out European patent, the competent national court otherwise — and it decides on the evidence the parties file, not on the figure stated in the initial letter.
Related
A related situation, where the risk sits on the buying side rather than the defending side: When a patent is offered to you for sale.
If a damages letter has landed on your desk, the first reply matters more than the final number in it. Send us the letter and the patent reference. We respond in minutes during business hours and confirm scope and price within one business day.