What is this page about: How to see when Light applies your custom FX rate versus the system rate, and the one rule that decides it.
On this page
- When custom rates apply vs system rates
- Where custom rates apply
- Where custom rates never apply
- The one rule to know: all-or-nothing per conversion
- Where to see this
- Related articles
When custom rates apply vs system rates
Quick answer: Light uses your custom FX rate for almost every transaction (bills, invoices, payments, expenses, and more). It falls back to the system rate only when a currency in the conversion is missing a custom rate for that period, or for a small set of areas that are designed to always use system rates, such as recurring-revenue reporting.
Where custom rates apply
Custom rates are used everywhere Light converts a foreign-currency amount. That includes:
- Bills
- Sales invoices
- Payments
- Bank reconciliation
- Expenses
- Credit notes
- Purchase-order matching
- Month-end FX revaluation
Where custom rates never apply
A few areas always use system rates by design, no matter what custom rates you've set:
- Background rate lookups
- Partner integrations and external rate feeds
- Spending-limit checks
- Recurring-revenue reporting (MRR)
Why recurring-revenue reporting is different: it intentionally stays on system rates so your historical trend doesn't shift every time you add a new custom rate.
The one rule to know: all-or-nothing per conversion
When Light converts between two non-EUR currencies (for example, USD to GBP), it checks both currencies for a custom rate before using either one.
- If both currencies have a custom rate set, the conversion uses custom rates.
- If only one currency has a custom rate set, Light uses system rates for the entire conversion. It never mixes one custom leg with one system leg.
- If the conversion involves EUR and one other currency, only that one other currency needs a custom rate. EUR is the reference currency, so a EUR-to-USD conversion just needs a USD rate.
To make sure your custom rates are used everywhere: set a rate for every non-EUR currency you transact in, for the period you're reporting on. If you set a rate for USD but not GBP, any USD-to-GBP conversion falls back to system rates for the whole conversion.
Where to see this
There isn't a standalone exchange-rates report today. The one place FX rates show up directly in the product is the Auto FX rate toggle in the Match difference dialog during bank reconciliation. When it's on, Light fetches a rate and converts the amount for you. If it can't fetch a rate, the toggle switches off and won't convert, and shows an alert icon with the tooltip "Failed to fetch exchange rates. Auto FX rate is disabled."
If a converted figure looks off, check whether a custom rate is set for that currency.