I've got an extension of time but no money for it

An extension of time gives you more time to finish. On its own, it does not settle whether more money is due, or how it should be worked out. The money still depends on the terms of your subcontract, the period adopted, the resources actually affected and what has already been paid elsewhere.

The usual shortcut is weeks granted times your tender preliminaries, the site running costs you priced. That may not match how your subcontract values the cost, or what was actually on site. The cost of running on and the cost of extra resources can fall in the same weeks. But the same cost must never be counted twice. Other causes, the steps you took to limit the cost, and credits all need checking too.

Treat the granted period as a guaranteed payment and the figure is easy to knock down. The job is to set the time decision beside the actual costs, and mark every assumption and specialist input.

Treat the extension of time as a decision about time. The money needs its own route under your subcontract and its own proof. Use the granted period for the cost. Then identify the staff, plant and site set-up actually kept on site because of it, from payroll and invoices, less anything already paid elsewhere. Do not multiply every granted week by your tender preliminaries and assume the total is payable. Build the cost up instead, so each period, resource and credit stays visible.

Delay & Disruption Claim builds that cost line by line and puts it to your main contractor. Whether the time was properly granted is not our call. That stays with whoever assesses time.