Structure that finance departments expect
- Engagement reference (matches the contract or SOW)
- Billing period, e.g. 'March 2026'
- Day rate × days worked, or deliverable-based lines
- Expenses itemized with receipts available on request
- PO number if the client works with purchase orders
- Tax ID and reverse-charge note for cross-border EU work
Working with purchase orders
Larger clients often cannot pay an invoice without a PO number. Ask for the PO before the engagement starts and put it in the invoice header — it can shave weeks off corporate payment cycles.
Retainer vs time-and-materials
Retainers bill a fixed monthly amount and are simplest to invoice; time-and-materials needs itemized time. Whatever you pick, mirror the wording of your contract so approval is automatic.
Frequently Asked Questions
What is a reverse charge invoice?
For cross-border B2B services in the EU, VAT is accounted for by the client under the reverse charge mechanism. The invoice states 'Reverse charge — VAT to be accounted for by the recipient' and shows both VAT IDs.
How detailed should time entries be?
One line per work package per week is usually enough. Extreme daily detail invites micromanagement; too little detail invites queries.