Project management fee on an extension: how much to charge

Published guides put a project management fee anywhere from about 3% to 15% of the build cost, and 10% is a figure builders often start from. Don't stop at the percentage. Check it against the hours you'll spend: on a 16-week, £120,000 extension, a 10% fee of £12,000 pays £75 an hour for 10 hours a week of your time.

What does a project management fee cover?

It covers the work of running the job rather than building it. When you're the main builder and also coordinate trades the client pays directly, or you manage the whole build on a cost-plus basis, the PM fee is how you get paid for that coordination.

What it shouldn't quietly absorb: design work, structural calculations, planning applications or party wall agreements. If you're asked to do those, price them separately or list them as exclusions. Our guide to exclusions and assumptions wording has lines you can copy.

How much should you charge for project management?

Start from a percentage, then check it against your hours. A percentage scales with the job, which clients understand. Your hours tell you whether it pays.

Published figures vary a lot. Homebuilding & Renovating, updated in August 2026, says independent project managers usually charge 3% to 7% of the build cost, or a monthly fee or day rate instead. An older self-build guide quotes 8% to 15% for a full management service. The spread reflects how much the manager does: a consultant who visits weekly does less than a builder who books every trade and orders every delivery.

One renovation and extension builder we spoke to, moving from straightforward building into design and build, discussed charging a PM fee of 10% of the build cost. That's a common figure. Whether it's the right figure depends on how long the job runs and how much of your week it takes.

Put your own numbers in. If the fee per hour comes out below what you'd earn on the tools, the fee is too low, the job is too long for the fee, or you've agreed to do more than the fee covers. The day rate here comes from our guide to overheads per man-day.

Should you charge a percentage or a fixed fee?

Use a percentage while the build cost is still moving, and a fixed fee once the scope is settled. Each has a weakness.

Whichever you choose, say what happens if the programme runs over for reasons outside your control. A line such as "if the programme extends beyond [16] weeks for reasons outside our control, the fee continues at £[750] a week" protects you.

Do you charge VAT on a project management fee?

If you're VAT-registered, yes. HMRC's VAT Notice 708 says architectural, surveying, consultancy and supervisory services are always standard-rated, and management fees paid to consultants are standard-rated too. The exception is design and build, where those services are only part of the contractor's single supply, so the whole supply follows the rate of the building work.

Most work on existing homes is standard-rated anyway, so on a typical extension the fee and the build both carry 20%. On zero-rated or reduced-rate work, such as some conversions, how you structure the contract changes the VAT. Ask your accountant before you quote.

How should you write the fee on the quote?

As its own line, with a short scope underneath. Clients pay a fee more readily when they can see what it buys.

PROJECT MANAGEMENT: £fee + VAT (10% of the build cost of £build cost)

This covers:
- Preparing and updating the build programme, shared with you weekly
- Booking and coordinating all trades, including those you pay directly
- Ordering materials and checking deliveries
- Up to 3 site visits a week and a weekly update by WhatsApp / email
- Booking building control inspections and dealing with their queries
- Pricing and recording any changes you ask for, before they're done
- Snagging and handover

Not included: design, structural engineering, planning or party wall matters.

If the build cost changes through agreed variations, the fee is adjusted at the same percentage.

Common questions