Crate hmrc_rates 

HMRC exchange rates with bundled history and exact GBP conversion.

One Rates value holds all four series HMRC has published: monthly customs/VAT rates (from 2014-02), spot and yearly-average rates for years ending 31 March / 31 December (from 2010-12), and the discontinued 2014–2016 weekly amendments.

use hmrc_rates::{Rates, YearMonth};
use rust_decimal::Decimal;

let rates = Rates::new(); // free: the tables are compiled-in statics
let rate = rates.monthly_rate("USD", YearMonth::new(2025, 8).unwrap())?;
let gbp = rate.to_gbp(Decimal::from(100)); // exact, unrounded

Rates are HMRC’s figures, i.e. currency units per £1. Conversion divides exactly, and the crate never rounds.

Lookups are strict. An unpublished period is an error, never a silently substituted older rate. Fallback is explicit, see Rates::monthly_rate_or_earlier.

Features

• std, bundled (default): the full history compiled in, no parsing or I/O at startup, ~450 KB of read-only data.
• http: a blocking Updater that fetches newly published periods, with an on-disk cache.
• serde: compact string forms ("2026-07", "USD", "monthly").
• cli: the hmrc-rates binary.

The core is no_std + alloc with only bundled enabled the crate builds on wasm32-unknown-unknown.

Structs

Currency

A three-letter currency code as published by HMRC.

ParseYearMonthError

The error returned when parsing a YearMonth from a string fails.

Rate

A resolved HMRC rate: currency units per £1, with exact Decimal arithmetic.

Rates

All HMRC rate tables: bundled data plus (with the http feature) fetched periods.

Table

A borrowed view of one period’s table — resolve once, convert many times.

YearEnd

A spot/average rate period: HMRC publishes these only for years ending 31 March or 31 December, so other dates are unrepresentable.

YearMonth

A calendar month, the key of HMRC monthly rate tables.

Enums

LookupError

Why a rate lookup failed.

Period

The period a Rate or table applies to.

RateType

The four rate series HMRC has published.