Why a currency converter for invoices is non-negotiable for international work
Sending a foreign currency invoice without a clear FX line is the freelance equivalent of leaving a tip jar out: the client decides what to pay. A proper currency converter for invoice work fixes that by anchoring three things — the amount, the exchange rate, and the date the rate was captured — before the invoice ever leaves your inbox.
Most freelancers learn this the expensive way. The first US client pays a EUR invoice via a Wise transfer that lands 3% short. The second client pays late, and by then EUR/USD has slid 1.5% the wrong way. By the third invoice, you have stopped trusting the deposit notification and started doing the FX math yourself. This tool is built for that third invoice — the one where you want a number you can defend, in writing, before the wire moves.
Which exchange rate source to use
There are three credible sources for the FX rate you put on an invoice:
- ECB euro foreign exchange reference rates. Published every working day at around 16:00 CET for 30 currencies. Free, dated, and treated as authoritative across the EU.
- OANDA daily rates. Bid, ask, and midpoint figures published daily on a UTC-midnight cycle. Widely used by accounting platforms and accepted by HMRC and the IRS.
- Your own bank's published rate. Less favourable than the mid-market rate, but the right choice if your client wires directly into your local account and you want the invoice to reflect what will actually settle.
Pick one source and stick with it across invoices. Switching between mid-market, bank, and PSP rates from one invoice to the next is a fast way to confuse both your client and your accountant.
Locking the rate at invoice date vs payment date
Accounting standards (US GAAP, IFRS, HMRC, IRS Publication 54) all default to the invoice-date rate when recording revenue in your home currency. The payment-date rate matters for one thing only: calculating the FX gain or loss between the booked figure and the actual settled amount.
That is why the invoice date in this tool is more than a label — it is the snapshot date for the rate you cite. Lock it once on the invoice, copy it into your bookkeeping, and treat any payment-day movement as a separate FX line in your books.
How to word the FX line on the invoice
Keep it short, dated, and traceable. The copy-ready line in this tool follows the pattern:
Invoice total: €1,000.00 (1 EUR = 1.0823 USD as of 2026-05-03) ≈ $1,082.30. Reverse rate: 1 USD = 0.9239 EUR.
That single sentence does four jobs at once: states the contractual amount in your currency, shows the rate, names the date, and gives the client the converted figure for budgeting. If you bill in the client's currency, flip the direction and add a one-liner: "Bank charges and FX margin to be borne by the sender."
Hidden bank fees and FX margins
The mid-market rate is what banks use between themselves. The rate they give you, as a small business or freelancer, is almost always 1–4% worse. Wise, Revolut, and modern PSPs trim that spread; legacy banks and PayPal widen it. The optional margin estimator in this tool exists for one reason — to remind you that the headline conversion is not what hits your account.
If the spread routinely matters (large contracts, monthly retainers in a foreign currency), two practical fixes help: hold a multi-currency account so you can convert on your schedule, or gross up the invoice by the expected margin and disclose it as a "cross-border processing fee" on the invoice line.
What to do if the rate moves before the client pays
You have three reasonable options, ordered from cleanest to messiest:
- Honour the locked rate on the invoice. Simplest and most professional. Any FX gain or loss is yours to absorb and book.
- Reissue the invoice with a new rate. Only do this if the contract explicitly allows rate adjustments and the swing is material (typically 2%+).
- Add a small FX adjustment line on the next invoice. Works for ongoing client relationships where small differences net out over time.
Whatever you choose, document it. The reason this tool exists — and the reason every invoice in InvoiceCat surfaces the FX line so prominently — is that the cheapest way to avoid an awkward conversation about exchange rates is to put the answer on the invoice before the question gets asked.
A quick note on tax and compliance
Tax authorities care about which rate you used and when. In most jurisdictions you must record revenue at the invoice-date rate in your functional currency, then reconcile the FX difference at payment. VAT rules in the EU and several other regions go further and require the rate source (ECB, national central bank, or HMRC's published rates) to appear on the invoice itself. This calculator handles the math; check your local tax rules before treating the output as final.