Construction retention calculator — percentage and NEC X16
Free, no sign-in. Nothing you type is stored or sent anywhere — it's all worked out in your browser.
Not legal or tax advice — check your contract. Your contract terms and the facts of your job can change the answer.
How this works
Percentage mode applies the retention rate to cumulative gross valuation and limits it to the entered £ cap or percentage of contract sum. The release split is editable; the default is half at completion and half at the end of the defects period.
NEC X16 applies the rate to Price for Work Done to Date above the retention free amount. The holding halves at Completion of the whole works or earlier take-over. The remaining half is released at the Defects Certificate.
These are cumulative holdings, not the incremental deduction on an individual payment. Compare with the previous certificate for an incremental amount.
FAQs
Is the release split always half and half?
No. The percentage mode starts at 50/50 but your contract can specify another split.
How does X16 use the retention free amount?
Only PWDD above that amount attracts retention, with a zero floor.
Does this show the current payment deduction?
It shows cumulative retention and releases. Compare previous certified retention to find the movement.
What releases NEC’s remaining retention?
The Defects Certificate, subject to the actual contract and amendments.
Civvio works this out automatically from your contract and site records.
Upload the contract and keep your diary, and Civvio flags the dates, notices and money at risk on every job — for you to review before anything is sent.
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