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Multi-Currency

SpeyBooks supports transactions in GBP, USD, and EUR with deterministic, auditable exchange handling.

Foreign-currency transactions are recorded explicitly and reported consistently in your base currency.

Supported currencies​

CurrencyCodeMinor unit
British poundGBPPence
US dollarUSDCents
EuroEURCents

All monetary values are represented in minor units.

Base currency​

Each organisation has a base currency (typically GBP for UK companies).

  • The base currency defines how reports are presented
  • All balances and reports are generated in the base currency
  • Foreign-currency transactions are converted deterministically

The base currency cannot be changed once the organisation is created.

Creating foreign-currency invoices​

Invoices can be issued in any supported foreign currency.

curl -X POST https://api.speybooks.com/v1/invoices \
  -H "Authorization: Bearer sk_live_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "contactId": "cont_17",
    "currency": "USD",
    "items": [
      {
        "description": "Consulting",
        "quantity": 1,
        "unitPrice": 200000,
        "vatRate": "zero"
      }
    ]
  }'

Response

{
  "success": true,
  "data": {
    "id": "inv_42",
    "invoiceNumber": "INV-0042",
    "currency": "USD",
    "subtotal": 200000,
    "vatAmount": 0,
    "total": 200000,
    "baseCurrencyTotal": 160000,
    "exchangeRate": 1.25,
    "createdAt": "2026-01-31T10:00:00Z"
  }
}

The invoice is recorded in the specified currency. Its base-currency value is derived using the applicable exchange rate.

Exchange rates​

SpeyBooks uses HMRC-published exchange rates for consistency and auditability.

Exchange rates are applied as follows:

  • At invoicing — used to calculate the base-currency value of the receivable
  • At payment — locked to the payment date

Exchange rates are stored alongside transactions and never recalculated.

Exchange gains and losses​

If the exchange rate changes between invoicing and payment, the difference is recorded automatically.

  • Exchange gain — you receive more base currency than expected
  • Exchange loss — you receive less base currency than expected

These amounts are posted to dedicated exchange gain or loss accounts.

Example​

  1. Invoice $2,000 at a rate of 1.25 → £1,600.00 expected
  2. Payment received at a rate of 1.20 → £1,666.67 received

Result: Exchange gain of £66.67

This gain is recorded automatically when the payment is posted.

Reporting​

All reports:

  • Are presented in the organisation's base currency
  • Apply exchange rates at the transaction date
  • Reflect realised gains and losses explicitly

No values are silently re-translated or normalised.

Key principles​

  • Currency is explicit on every transaction
  • Exchange rates are deterministic and stored
  • Gains and losses are accounted for, not hidden
  • Reports reflect ledger state exactly

Multi-currency handling in SpeyBooks is designed to be predictable, inspectable, and auditable.