Quantum calculator
Part 36 calculator
The cost and interest consequences of Part 36 offers under CPR 36.17 in England and Wales. The additional amount and the enhanced interest are computed from the published rule, shown with their full working, and cited to source. Costs are never quantified; the indemnity costs and CPR 36.17(3) consequences are narrative outputs with the date split computed.
Rules current to 6 April 2021. Read how these calculators work on the quantum methodology page.
What CPR 36.17 consequences are
Part 36 is a self-contained code of settlement offers with automatic consequences (Gibbon v Manchester City Council [2010] EWCA Civ 726). Where a claimant obtains a judgment at least as advantageous as its own Part 36 offer, CPR 36.17(4) requires the court, unless it considers it unjust under CPR 36.17(5), to order enhanced interest on the sum awarded, indemnity costs from expiry of the relevant period, interest on those costs, and an additional amount of 10 per cent of the first £500,000 plus 5 per cent of any amount above that, capped at £75,000.
Some elements are fixed and some are discretionary. The tier formula and its cap, the day count from the day after expiry of the relevant period through the judgment date inclusive, and the 21 day minimum relevant period under CPR 36.5 are deterministic and this calculator computes them. The level of any enhancement up to the 10 point maximum above base rate, whether the offer was a genuine attempt to settle, and whether an order would be unjust are judicial questions the calculator flags and never computes.
The historic Bank of England base rate series is not yet loaded into the rate store, so the base rate over the accrual window is an input you supply and must verify against the series published by the Bank of England. Where the window spans a base rate change, run a separate calculation for each rate period. The commencement dates of CPR 36.17 and CPR 36.5 in their current form are also awaiting verification at source, so their citations are shown without an in-force date. The direct URL for CPR Part 36 on justice.gov.uk is awaiting verification too, so citations link to the Civil Procedure Rules index on justice.gov.uk until it is verified.
Primary sources
- Civil Procedure Rules, as published on justice.gov.uk. CPR Part 36 contains CPR 36.5, CPR 36.17, and CPR 36.23; the direct Part 36 URL is to be verified on justice.gov.uk before publication.
- Gibbon v Manchester City Council [2010] EWCA Civ 726, Part 36 as a self-contained code.
- Telefonica UK Ltd v Office of Communications [2020] EWCA Civ 1374, the enhancements are cumulative and the additional amount is all or nothing.
- Barry v Barry [2025] EWHC 819 (KB), the full £75,000 additional amount awarded.
- Gohil v Sainsbury's and Rawbank v Travelex, the genuine attempt to settle question is fact-sensitive.
Frequently asked questions
What happens when a claimant beats its own Part 36 offer?
Under CPR 36.17(4) the court must, unless it considers it unjust, order interest on the sum awarded at up to 10 per cent above the Bank of England base rate from expiry of the relevant period, costs on the indemnity basis from expiry of the relevant period, interest on those costs at up to 10 per cent above base rate, and an additional amount calculated from the sum awarded.
How is the Part 36 additional amount calculated?
The additional amount under CPR 36.17(4)(d) is 10 per cent of the first £500,000 of damages plus 5 per cent of any amount above £500,000, capped at £75,000. The cap is reached at awards of £1,000,000. For non-money claims the percentages apply to the costs awarded. The additional amount is all or nothing, and the enhancements are cumulative, not mutually exclusive (Telefonica v Ofcom [2020] EWCA Civ 1374). The tiers remain operational; Barry v Barry [2025] EWHC 819 (KB) awarded the full £75,000.
What happens when a claimant fails to beat a defendant's Part 36 offer?
Under CPR 36.17(3) the claimant pays the defendant's costs from expiry of the relevant period plus interest on those costs, and recovers its own costs up to expiry. This calculator computes the date split and presents the consequence as a narrative. It never quantifies costs.
Does Part 36 apply on the small claims track?
No. Part 36 does not apply on the small claims track. The calculator gates small claims matters and returns no consequences for them.
How long must the relevant period be?
At least 21 days under CPR 36.5. The calculator validates the entered period and flags anything shorter. CPR 36.5(5), in force from 6 April 2021, also permits an offer to provide for interest to accrue after the relevant period, which the calculator notes but does not compute.
Are the enhanced interest rates automatic?
No. The enhanced rates under CPR 36.17(4)(a) and (c) are discretionary maxima of up to 10 percentage points above the Bank of England base rate, not fixed entitlements. You enter the enhancement and the calculator caps it at 10. Whether the offer was a genuine attempt to settle (Gohil v Sainsbury's; Rawbank v Travelex) and whether an order would be unjust under CPR 36.17(5) are judicial questions the calculator flags and never computes.