If your business invoices customers in US dollars, buys stock from a supplier in euros, or holds a foreign loan, you have probably noticed something frustrating: the same invoice can show a different value in your accounts depending on when you look at it. An unpaid £39,000 invoice can turn into a £37,800 receivable on paper, with no extra product shipped and no discount given. For SME owners and finance teams, this creates confusion at month-end and real anxiety at year-end, when the accountant asks for ‘the closing rate’ and books a loss or gain that seems to appear from nowhere. Understanding how IAS 21 (for IFRS reporters) and FRS 102 Section 30 (for UK GAAP reporters) require you to record and revalue foreign currency transactions removes that mystery — and lets you explain the movement to your bank, your board, or HMRC with confidence.
What IAS 21 and FRS 102 Section 30 Actually Require
Both standards say broadly the same thing, because FRS 102 Section 30 was built on the same principles as IAS 21. When you enter into a transaction in a foreign currency — say, you raise a sales invoice in US dollars — you translate it into sterling using the exchange rate on the transaction date, known as the spot rate. That sterling figure is what goes into your revenue and your debtor ledger. The complication arises because that invoice might not be paid straight away. If it is still outstanding at your year end, the rules require you to look at it again and ask: what would this dollar amount be worth in sterling today? If the rate has moved, the sterling value of the debt has moved with it, even though the dollar amount on the invoice has not changed by a single cent.
Monetary vs Non-Monetary: The Distinction That Decides Everything
The single most useful idea in this area is the split between monetary and non-monetary items. Monetary items are things that will be settled in a fixed amount of currency — cash in a dollar bank account, a trade receivable from a US customer, a loan from a euro-denominated lender. Because the amount you will eventually receive or pay is fixed in foreign currency, its sterling equivalent genuinely does change as rates move, so these items are retranslated at every balance sheet date using the closing rate. Non-monetary items are different: stock you bought in dollars, a machine you purchased from Germany, a prepayment you made in euros. These are not going to be settled in cash later; they represent physical assets or rights to receive goods or services rather than a right to receive or pay cash, so items carried at historical cost stay at the rate that applied when you first recorded them and are not retranslated each year end.
| Item type | Examples | Year-end treatment |
|---|---|---|
| Monetary items | Cash in foreign currency, trade receivables and payables, foreign currency loans | Retranslate at the closing rate on the balance sheet date; the resulting gain or loss goes to profit and loss |
| Non-monetary items | Inventory, property, plant and equipment, prepayments made in foreign currency | For items carried at historical cost, keep at the rate applied on the original transaction date; no retranslation (subject to normal impairment or net realisable value rules) |
Practical tip: for day-to-day transactions, most bookkeeping software will apply the rate on the invoice date automatically. FRS 102 and IAS 21 both allow you to use an average rate for a period — for example, a monthly average — if exchange rates are not fluctuating significantly, which saves time without breaching the standard.
Worked Example: A $50,000 US Invoice
Suppose your company, a UK-based software reseller, invoices a customer in New York for $50,000 on 1 October. On that date, the exchange rate is £1 = $1.28. Three months later, at your 31 December year end, the invoice is still unpaid, and the pound has strengthened against the dollar, with the closing rate now £1 = $1.32. Here is how the transaction moves through your books, step by step.
| Invoice amount raised on 1 October | $50,000 |
| Exchange rate at invoice date | £1 = $1.28 |
| Sterling value recognised at invoice date ($50,000 ÷ 1.28) | £39,062.50 |
| Exchange rate at year end, 31 December | £1 = $1.32 |
| Sterling value of the same $50,000 at year end ($50,000 ÷ 1.32) | £37,878.79 |
| Foreign exchange loss to be recognised in profit and loss | £1,183.71 |
| Account | Dr | Cr |
|---|---|---|
| Trade receivables — US customer | £39,062.50 | |
| Revenue | £39,062.50 |
Recognise the sale at the spot rate on the invoice date, 1 October, when £1 = $1.28.
| Account | Dr | Cr |
|---|---|---|
| Foreign exchange loss (profit and loss account) | £1,183.71 | |
| Trade receivables — US customer | £1,183.71 |
Retranslate the outstanding receivable at the closing rate on 31 December, when £1 = $1.32. The dollar amount owed by the customer has not changed, but its sterling value has fallen.
Do not treat foreign exchange gains and losses as just a reporting curiosity. For UK corporation tax purposes, most exchange differences on monetary items that run through your profit and loss account are taxable or allowable in the same period, under the loan relationships and related rules administered by HMRC. An unrealised FX loss on a trade debtor can genuinely reduce your taxable profit before you have lost any cash, and an unrealised gain can increase it before you have banked anything. Talk to your accountant about how these movements feed into your tax computation, particularly if the currency you deal in is volatile.
What This Means for Your Numbers
The practical impact is that your reported profit can move up or down purely because of exchange rate changes, with no change in the underlying business activity. This is why many finance teams separate trading profit from FX gains and losses in their management accounts, so that a board or lender can see performance excluding currency noise. It also means that if you invoice heavily in foreign currency, your year-end debtor and creditor balances need a proper retranslation exercise before the accounts are finalised — missing this step is one of the most common errors found in SME accounts during an audit or accountant’s review, because the balance sheet ends up out of step with the actual spot rate on the reporting date.
Key Takeaways
- Record every foreign currency transaction at the spot rate on the transaction date — an average rate is acceptable only if exchange rates are not moving significantly during the period.
- At each year end, retranslate monetary items only (cash, receivables, payables, loans) using the closing rate; leave non-monetary items carried at historical cost, such as stock, fixed assets, and standard prepayments, at their original transaction date rates.
- Expect the resulting exchange gain or loss to hit your profit and loss account, and check with your accountant how it flows through your corporation tax computation.
- If foreign currency trading is a regular part of your business, ask your finance team to report trading profit and FX movements separately in management accounts, so performance is not obscured by rate swings.
Need help getting foreign currency accounting right?
Our team can review your FX transaction processes, set up correct retranslation procedures under IAS 21 or FRS 102, and make sure your management accounts separate trading performance from currency noise.
