Building Surveyor Salary Index

Liquidated damages calculator

Last reviewed September 2026

Work out liquidated damages for late completion under the JCT contracts: the period of delay, the amount, the reduction when the employer takes part of the works early, and what’s repaid if a later extension of time moves the completion date. It also lists the notices the employer needs before it can deduct them.

Contract and dates

Parts taken into possession early (optional)

If the employer takes possession of part of the works before practical completion, the rate reduces from that date by the same proportion as the part’s value bears to the Contract Sum.

Enter the Completion Date, practical completion and the rate to see the damages.

Before the employer deducts

  • The Architect/Contract Administrator has issued a Non-Completion Certificate. A later extension of time cancels it, and a further certificate is needed if the works are still late.
  • Before the date of the Final Certificate, the Employer has told the Contractor in writing that it may require payment of, or withhold or deduct, liquidated damages.
  • The Employer gives notice requiring payment or stating that it will withhold or deduct, no later than 5 days before the final date for payment of the amount under the Final Certificate.
  • To deduct from a payment, the Employer gives a pay less notice in time for that payment, stating the rate and period.

Use the payment notice calculator to find the last day for a pay less notice.

How it’s worked out

  • Damages run in calendar days, weekends and bank holidays included, for each day after the Completion Date up to and including practical completion.
  • A weekly rate is divided by 7 for part weeks. That’s the usual reading of “per week”; a contract that says “per week or part thereof” charges a part week in full.
  • Partial possession reduces the rate from the date possession is taken, by the part’s share of the Contract Sum. Minor Works doesn’t provide for partial possession.
  • Where the works are divided into sections, each with its own completion date and rate, work each section out separately.

Before you rely on the figure

This calculator is a guide, not legal advice. Check the rate, the dates and the notice rules in your contract, including any amendments such as a cap on damages. Liquidated damages are usually enforceable unless they’re out of all proportion to the employer’s legitimate interest in the works finishing on time, following the Supreme Court in Cavendish Square Holding v Makdessi.

Sources

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