Invoicing for contractors: what changes

Contractors invoice like anyone else — number, dates, lines, tax, total — but day rates and materials on the same job needs care. The recurring problem: day rate versus fixed price has to be agreed before day one, not argued at invoice time.

Where it goes wrong

Day rate versus fixed price has to be agreed before day one, not argued at invoice time. Almost every dispute I have seen in this category traces back to something that was agreed verbally and never written down, then remembered differently by two people with different incentives.

The fix is upstream

Write the scope into the quote, get it accepted in writing, and convert that accepted quote straight into the invoice so the billed work and the agreed work are provably the same document.

Keep the records

Whatever the size of the work, the income is declarable and the records have a retention period — usually five to seven years.

Know who your customer actually is

If you are working through an agency, your customer is the agency and not the end client, however much time you spend on their site. That determines whose name goes on the invoice, whose payment terms apply and who you chase. Billing the end client directly when the contract is with the agency produces a document nobody can pay.

Timesheets gate the payment

On most contract work the invoice cannot be processed until a timesheet is approved, and the approver is usually a manager with other priorities. That means your payment depends on an action by someone who has no stake in your cash flow.

Submit the timesheet the moment the period closes, and chase the approval rather than the invoice. Chasing a finance department about an invoice that is waiting on an unapproved timesheet wastes a week and makes you look like you do not understand the process.

The payment cycle is longer than it sounds

"Weekly payment" commonly means the week ends Sunday, timesheets are approved Monday or Tuesday, the invoice is raised, and payment follows on the agency's own terms. Four to six weeks from starting to first payment is entirely normal and it catches out anyone who budgeted for a fortnight.

Ask before you start: when does the period close, when are timesheets approved, when is the payment run, and when will the first payment actually land. Plan around the answer rather than the headline.

Purchase orders and reference numbers

Contract work is where automated invoice rejection is most common. Missing PO number, wrong cost centre, a name that does not match the supplier record — any of these causes a silent rejection that you only discover by chasing. Get the exact reference format in writing at the start and put it on every invoice unchanged.

Rate, expenses and what is included

Nail down before day one whether the rate is inclusive of holiday, whether travel to site is billable, what the expense policy is, and whether there is an overtime rate. These are frequently vague at agreement stage and completely specific at dispute stage. An email confirming them is worth more than a conversation.

Employment status and payroll deductions

Several countries have rules determining whether a contractor is really employed for tax purposes — IR35 in the UK, similar tests in Australia, the Netherlands and the US. The outcome can change what your client may pay you gross and what must go through payroll, and in construction there are withholding schemes that deduct tax before you are paid whatever your invoice says.

This affects what lands in your account rather than what your invoice says, and it is worth understanding before the first payment rather than after a shortfall.

Keep your own record of hours

Independent of whatever system the client uses. Portals change, access is revoked when a contract ends, and a dispute about hours worked eight months ago is unwinnable without your own contemporaneous record. Your invoices are part of that record, which is an argument for them living somewhere you control rather than in an agency portal you will lose access to.

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