How consultants should invoice: a practical guide

Retainers in advance for the coming period; project fees against named deliverables, not against elapsed months. Itemise labour and materials separately, put a real due date on it rather than "on receipt", and send it as a PDF the client can forward to whoever actually pays. For consultants, the detail that matters most: retainers invoiced in advance need the period stated — "October retainer" not just "retainer".

How to price the work

Retainers for ongoing work, fixed fees for defined deliverables, day rates only where the client controls the schedule. Hourly billing for senior advisory work signals that you sell time rather than judgement.

What the lines should look like

For a retainer, a line that reads well is:

Advisory retainer, October, up to 10 hours

Specific enough that the person approving payment — often not the person who hired you — can see what they are paying for. Here is the same job as a finished invoice line:

Advisory retainer — October
Up to 10 hours; 7.5 hours used, unused hours do not carry forward — £1,500.00

Deposits

Retainers are billed in advance for the coming period. Project work commonly splits 50/50 or into thirds against milestones.

Materials and markup

Travel and subsistence should be agreed in advance with a policy — economy flights, standard-class rail, a cap on hotels — and billed at cost with receipts. Unagreed expenses are the most-queried line on any consulting invoice.

The mistake consultants make most

Retainers invoiced in advance need the period stated — "October retainer" not just "retainer".

What a retainer buys. "October retainer" on its own is a bill for nothing visible. Name the period and the scope — "up to 10 hours advisory, October" — so the client can see what lapsed and what did not.

Say what the retainer bought

"October retainer — £1,500" is a bill for nothing visible, and it is the first line questioned when a client reviews costs. "Advisory retainer, October, up to 10 hours; 7.5 used" is a bill with a scope, a period and evidence. Name whether unused hours carry forward, too — the assumption that they do is the most common source of friction in retained work, and it costs nothing to settle in advance.

Getting paid, in this trade specifically

Corporate clients pay on terms through a portal and need a PO on the invoice. The delay is almost never unwillingness — it is an unapproved timesheet or a missing reference, and the fix is to ask which of the two it is rather than asking for payment.

The rest is the same for everyone: what has to be on the document, how to number it, how to chase it and how long to keep it. If you are registered for tax, the rate and the label depend on your country.

EstimateBill tracks what is unpaid, reminds you on the due date, and writes the follow-up message for you in three tones. See how the reminders work.