Multi-currency invoicing for firms with international clients

The first time a professional services firm invoices a client in a different currency, the instinct is usually to convert. The engagement is in dollars, your rates are in pounds, so you find the exchange rate, do the maths, and send a sterling invoice for the converted amount.

This is almost always the wrong approach. Here is a more principled way to handle multi-currency billing — and the complications you need to account for when working across borders.

Why FX conversion on invoices is usually wrong

When you convert a fee to your home currency before invoicing, you take on the currency risk. The client agreed to a fee in their currency; you're now invoicing them in yours. If the rate moves between engagement and payment, one of you absorbs the difference. Usually it's you, because clients don't pay faster when the rate moves against them.

The cleaner approach: denominate the invoice in the client's agreed currency and receive payment in that currency. You take the FX hit when you convert to your home currency for your own accounts, but you control the timing of that conversion. More importantly, you invoice for what the client expects to pay, which removes one potential point of friction.

This requires a bank account (or a Wise/Airwallex multi-currency account) that can receive the relevant currencies. The setup cost is a few hours. The operational benefit of not negotiating "but the rate has changed" with clients every quarter is worth it.

Set a default currency per client and never override it mid-engagement

Every client in your billing system should have a default invoice currency locked at the start of the engagement. Once set, every invoice for that client — scheduled, on-completion, or manual — goes out in that currency at the agreed rate. You don't recalculate, you don't convert, you don't adjust for the spot rate.

If you need to change the currency (the client reorganises their billing entity, they move from US to Canada, whatever), treat it as a new engagement with a new agreement. Don't change mid-stream without written confirmation.

This matters more than it seems. A client who has budgeted £5,000/month for your retainer is budgeting in pounds. If you start invoicing in dollars because your rates changed, you've created a budget problem for them that has nothing to do with the value of your work.

Keeping currencies separate in your reporting

The most common multi-currency accounting mistake is summing revenue across currencies. If you have three clients paying in USD, two in GBP, and one in EUR, your total revenue is not the sum of all those numbers. You have three separate revenue streams that happen to be denominated in different currencies.

Reports should always group by currency first. USD revenue, GBP revenue, EUR revenue — three separate totals. Only then, for management reporting purposes, do you convert to a base currency for aggregation, using a fixed rate for the reporting period (monthly average or period-end rate, consistently applied).

The same applies to outstanding invoices (debtors by currency), retainer balances (a client's pre-purchased hours pool is always in the currency they paid), and payment reconciliation. Mixing currencies in a single ledger without clear denomination leads to reconciliation errors that become expensive to unwind.

The tax complications of cross-border professional services

This is where things get genuinely complicated, and where the stakes are high enough that getting it wrong creates real tax liability.

UK to EU (B2B): VAT reverse charge. If you're a UK VAT-registered firm supplying professional services to a business in an EU member state, the supply is generally outside the scope of UK VAT (the place of supply is where the customer belongs). You issue an invoice without UK VAT and include the statement: "VAT zero-rated — customer to account for VAT under the reverse charge mechanism." The EU client accounts for VAT in their own jurisdiction.

If the EU client is a consumer (not a business), the rules are different — you may need to register for VAT in their country or use the One Stop Shop (OSS) scheme. For professional services firms, B2C cross-border supply is less common but worth verifying.

UK to US: no VAT. The US does not have a federal VAT. Your UK invoice to a US client has no UK VAT and no US equivalent. The client may have state-level sales tax obligations on certain services, but that's their compliance issue, not yours. Invoice without VAT, note that the supply is outside the scope of UK VAT.

Canada: GST/HST considerations. Canadian firms invoicing across provinces need to apply the correct GST/HST rate for the province where the client is located. Invoicing into the US from Canada follows similar logic to the UK position — no GST/HST on exports of services to non-residents.

When you have clients in multiple countries, the practical approach is: understand the rules for your most common client jurisdictions (usually 2–3 countries), configure your billing system with the correct tax treatment per client, and engage an accountant with cross-border professional services experience to review once a year. The rules change — particularly anything connected to digital services in the EU.

What goes on the international invoice itself

Beyond the standard invoice fields, cross-border invoices need:

Currency clearly stated. Not just the number — the ISO currency code or symbol, unambiguously. "5,000" means nothing. "USD 5,000" or "£5,000 GBP" is clear.

The applicable VAT/tax treatment. Either the rate and amount of tax charged, or a statement explaining why no tax is charged (zero-rated export, reverse charge, outside scope). Don't leave it blank — blank looks like an error.

Your bank details for the correct currency. If the client is paying in USD, give them your USD banking details. If they're paying in GBP, your GBP details. Clients who receive a GBP invoice but only have USD details end up converting unnecessarily and you absorb the bank's spread.

Payment reference. Tell the client what to put in the payment reference. For international wires, references frequently get dropped or truncated. If your accounts receivable reconciliation depends on a reference number, communicate that explicitly.

Getting paid faster in foreign currencies

The single most effective change: accept payment in the client's currency through a multi-currency business account rather than asking them to convert. Wise Business, Airwallex, and Revolut Business all offer local receiving accounts in major currencies — you get a local sort code and account number for GBP, a routing number and account for USD, an IBAN for EUR. Clients pay via local bank transfer (fast and cheap) rather than international wire (slow and expensive).

For clients paying in CAD or AUD where you don't have local accounts, consider whether the client would prefer to pay via credit card through a payment portal — the FX cost is theirs, the settlement is fast, and the reconciliation is automatic.

The other lever is payment terms. Net 30 is standard in North America; net 14 or net 7 is more common in the UK. If you're billing a US client on UK terms, they may pay on US terms regardless. Agree the terms explicitly rather than relying on your invoice defaults.

For large or new international clients, a deposit upfront (25–50% of the engagement value) significantly reduces the risk of a slow-pay or no-pay situation. Cross-border legal remedies are possible but expensive. A deposit is a better risk management tool than hoping international clients follow UK payment norms.