GDT Exchange Rate Rules: Handling Weekend and Public Holiday Invoicing
RielSync Team · 6 min read · Updated August 31, 2026
In short
Cambodian self-assessment taxpayers must use the NBC daily rate (or a market rate no lower than it) for KHR invoices. When an invoice is issued on a weekend, public holiday, or before NBC publishes that day's rate, GDT guidance says to use the NBC rate from the previous business day instead. This is our reading of published tax guidance, not tax or legal advice; confirm your own filings with an accountant or the GDT directly.
The rule Cambodian businesses are expected to follow for KHR invoicing comes from Instruction No. 26118 GDT, issued by the General Department of Taxation (GDT) on 28 October 2022, which replaced an earlier instruction (10362 GDT, 17 May 2022). It sets the National Bank of Cambodia's (NBC) daily official rate as the reference for self-assessment taxpayers' KHR invoicing, and it says what to do on a day NBC hasn't published one yet.
The daily rule
On a tax invoice showing Khmer Riel, the conversion rate used cannot be lower than NBC's official daily rate for that day. A business can use its own rate for pricing, menus, or a cash register, but the rate that ends up on the tax invoice has to be at least the NBC figure.
The weekend and holiday fallback
NBC publishes its rate on working days, typically in the late afternoon. That leaves a gap: weekends, public holidays, and any invoice issued before that day's rate is out. For those cases, the guidance is to use NBC's rate from the immediately preceding business day, rather than leaving the rate undefined or guessing at one.
- 01Invoice issued on a normal working day, after NBC has published: use that day's NBC rate.
- 02Invoice issued on a weekend or public holiday: use the NBC rate from the last business day before it.
- 03Invoice issued before NBC has published that day's rate: use the previous business day's rate.
Why this matters for automated sync
A system that only records a rate on the days NBC actually publishes, and does nothing on the days it doesn't, matches this rule by default: the last recorded rate is already the correct previous-business-day figure to fall back on. That is the approach RielSync takes. See how often the NBC rate actually changes for what that gap pattern looks like across a full year.
Sources
Instruction No. 26118 GDT (28 October 2022), General Department of Taxation, "The Use of Exchange Rates for Self-Assessment Taxpayers," via tax.gov.kh. Corroborating commentary from DFDL and VDB Loi. This reflects our reading of that guidance and professional commentary on it, not tax or legal advice specific to your business; confirm your own filings with an accountant or the GDT directly.
FAQ
What exchange rate should a Cambodian business use on a KHR invoice?
The NBC daily official rate, or a market rate no lower than it, per Instruction 26118 GDT (28 October 2022).
What rate applies on a weekend or public holiday?
The NBC rate from the immediately preceding business day, since NBC doesn't publish on non-working days.
Is this the same instruction that's been in force since 2022?
Instruction 26118 GDT replaced an earlier instruction (10362 GDT) in October 2022. We found no evidence of a further superseding instruction as of this writing, but Cambodian tax guidance can change, so confirm current applicability with an accountant or the GDT before relying on it for a filing.