Progress Invoicing With Retention, the Way UK Contractors Actually Need It

Claim by percentage across a job, hold retention at the rate you set, see the exact amount due, with reverse charge VAT and CIS handled. Every figure reconciles.

What most tools get wrong

Interim applications and retention are where most field service tools let UK contractors down.

You win a job through a main contractor. The QS wants a monthly application for payment, not a regular invoice. Scope line by scope line, percentage complete, this period, retention deducted, net now, remaining. Cumulative this period must agree with what was previously certified. Reverse charge or CIS may apply, depending on the job.

Your invoicing tool can produce an invoice. That is not what is being asked for.

So most contractors do it on a spreadsheet, send it to the accountant to invoice from, or submit through the main contractor's portal and keep no working copy of their own. Each option breaks at the same point: when something does not tie out and the application gets rejected, you are reconstructing the maths by hand under time pressure.

How it works

You set a retention rate once at job level. Each application is built from scope lines, where you enter the percentage complete this period, either per line or across the whole job.

The system fills in the rest. Contract value per line, claimed before, the value being claimed this period, retention deducted, net now, remaining.

Worked example, from a job with four scope lines totalling £400.40 on the contract. Certify 50% complete across the job and the system computes £200.20 gross certified this period, deducts 10% retention (£20.02), shows £180.18 net, adds VAT at 20% (£36.04), and gives a due figure of £216.22 on this application. Every figure reconciles.

Retention is held against the job at the rate you set. Once every line has been certified to 100%, you release it on one invoice, with the figures already there. Field Forge does not split the release between practical completion and the end of the defects period.

Every application is kept as a permanent, dated record. The next application opens with these figures already sitting in Claimed before. No more "what did we claim last month" with the spreadsheet open in the next window.

The AI suggests, the system calculates

The maths on an application is not a place for guesswork. The AI does not touch any figure that lands on the application: not the line totals, not the retention deduction, not the VAT, not the CIS amount, not the final due figure.

A deterministic engine computes every total. The AI is not in this loop at all. We are not interested in shipping a tool that lets a language model decide what your customer owes you this month.

Reverse charge and CIS, handled in line

If the domestic reverse charge applies to the job, the VAT treatment is reflected per line and the application carries the correct wording. If a CIS deduction applies, it is calculated and shown on the application rather than worked out on the side.

The same logic feeds whatever invoice goes alongside the application, so the figures going out and the figures on your accounts stay aligned.

Who it's for

If you are moving from domestic work into commercial or fit-out, and the main contractor's QS has asked for an application for payment instead of an invoice, this is built for you. Mechanical and electrical subbies, fit-out crews, smaller builders winning main-contractor work. Plumbers, electricians, gas engineers, builders. Sole traders up to firms of around 200 staff.

Field Forge is the AI-native operating system for UK trade contractors. Start a free 30-day trial at fieldforge.io.