Works out what follows from an unaccepted or late-accepted Part 36 offer under CPR Part 36 (England and Wales): the additional amount, enhanced interest, and interest on costs. Everything runs in your browser — no figure you type is sent anywhere or stored.
Part 36 does not bite in every case, and the fixed-costs rules changed on 1 October 2023. Answer these and the calculator will tell you which regime applies.
The first day of trial is the first day the parties are required to attend court; judicial pre-reading days do not count (Mate v Mate [2023] EWHC 806 (Ch); Gagliardi v Evolution Capital Management LLC [2025] EWHC 3488 (Comm)).
Judgment against the defendant is at least as advantageous to the claimant as the proposals in the claimant’s own Part 36 offer. The court must make the orders in r.36.17(4) unless it considers it unjust to do so.
An offer is made when it is served, not when it is received (r.36.7(2)); use the date of deemed service under CPR 6.26.
Costs from expiry of the relevant period are on the indemnity basis (r.36.17(4)(b)) and are for assessment. If you have a figure, the interest on them can be estimated.
In a fixed-costs claim, r.36.24(4)–(5) replaces indemnity costs with additional costs of 35% of the difference between the fixed costs for the stage applicable when the relevant period expired and the stage applicable at judgment. Take both figures from Table 12, 14 or 15 in Practice Direction 45.
The claimant fails to obtain a judgment more advantageous than the defendant’s Part 36 offer. The court must, unless it considers it unjust, order that the defendant is entitled to costs (including any recoverable pre-action costs) from expiry of the relevant period, and interest on those costs: r.36.17(3).
What r.36.17(3) does and does not do. It gives the defendant its costs from expiry, and interest on them. It says nothing about the claimant’s own costs up to expiry — those follow from the general discretion in r.44.2.
In a fixed-costs claim, r.36.24(2) and (9) fix both sides. The claimant takes the fixed costs for the stage applicable when the relevant period expired; the defendant takes the fixed costs applicable at the date of judgment, less the claimant’s. Take both figures from Table 12, 14 or 15 in Practice Direction 45.
The offer was accepted. The consequences are in r.36.13 — or r.36.23 where fixed costs apply.
Acceptance carries no enhancement. Enhanced interest, indemnity-basis costs and the additional amount all belong to r.36.17, which applies on judgment being entered. None of them arises on acceptance, however late.
Fixed costs, r.36.23. Take the figures from Table 12, 14 or 15 in Practice Direction 45.
Every consequence above is subject to this. In considering whether it would be unjust, the court must take into account all the circumstances, including the five matters in r.36.17(5):
The burden is on the party resisting the usual order and it is a formidable one (Smith v Trafford Housing Trust, approved in Webb v Liverpool Women’s NHS Foundation Trust [2016] EWCA Civ 365). The court may find it unjust to make some but not all of the r.36.17(4) orders, though it would be unusual (JLE v Warrington & Halton Hospitals NHS Foundation Trust [2019] EWHC 1582 (QB)).
A plain-text record of the inputs, the working and the caveats. Select all and copy.
A calculation aid, not legal advice. It does not create a solicitor–client relationship, and no reliance should be placed on it without advice on your own case. Every figure is a draft for review by a qualified solicitor or barrister.
Each consequence applies only unless the court considers it unjust (rr.36.13(5), 36.17(3), 36.17(4)). Enhanced interest is shown as simple interest pro-rated on a 365-day year; the rate is a matter for the court’s discretion. The additional amount under r.36.17(4)(d) is 10% of the first £500,000 and 5% of any excess, capped at £75,000 — thresholds set by s.55 Legal Aid, Sentencing and Punishment of Offenders Act 2012 and the Offers to Settle in Civil Proceedings Order 2013 (SI 2013/93), and not index-linked.
Scope. This assumes a single claimant and a single defendant at first instance, with unrestricted recovery of costs. It does not cover periodical payments (r.36.18), provisional damages (r.36.19), deductible benefits (r.36.20), costs limited to court fees (r.36.21), Protocol offers in RTA and EL/PL claims (rr.36.25–36.31), counterclaims and Part 20 parties, or offers made in appeal proceedings (r.36.4).
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Written with AI. This tool was written with the assistance of AI (Anthropic’s Claude) and then checked against the rule text and the judgments cited. AI-drafted material can be wrong, incomplete or out of date, and can be confidently mistaken; nothing here has been settled by counsel or tested in court. Every figure is a draft for review by a qualified solicitor or barrister before it is relied on.
Author. Written and published by Serhan Handani in a personal capacity. It is not the work of, and does not represent the views of, any firm. For contact details, or to report an error in the rules or the arithmetic, see handani.dev.
Source and copyright. The rules applied are the Civil Procedure Rules 1998 (SI 1998/3132) as revised, read from legislation.gov.uk. The Civil Procedure Rules are Crown copyright, and this page contains public sector information licensed under the Open Government Licence v3.0. The rules are paraphrased here rather than reproduced, no practitioner commentary is quoted, and cases are named only where a judgment determines a figure the page uses.
Version · CPR Part 36 checked as at , against the revised Civil Procedure Rules 1998 (SI 1998/3132) current to · Bank Rate data verified as at .