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Effective dates

Sales tax rates have effective dates. A jurisdiction announces a rate change months in advance; we load the new file as soon as it’s published; the new rate takes effect on its effective_from date.

Refresh cadence. State DoR publications are pulled weekly (Saturday evening ET). Weekly cadence sits comfortably inside the quarterly cadence at which rates actually change, so new files land well before the effective date in most cases.

The as_of parameter. Pass as_of=YYYY-MM-DD to query the rate in effect on a specific date. Required when:

  • Recomputing tax for a refund or return at the rate that was effective when the original transaction happened
  • Auditing historical tax payments against current rates
  • Comparing rate changes across periods

effective_from and effective_to are returned on each row when the state’s rate data carries effective-period detail. They bound the period the row’s rate applies to:

row.effective_from   # date(2026, 4, 1) — Q2 starts
row.effective_to     # date(2026, 6, 30) — Q2 ends

States that store rates as a current snapshot only (NM, MO, IL, CO, LA, AL, AZ, AK at the state level) return the current rate regardless of as_of; historical queries against them are unsupported until those publications are backfilled.

Pre-history queries. When as_of predates the earliest loaded period for the state, the API falls back to the oldest available row and logs a warning internally. The response is still returned; ops is alerted to the coverage gap.

Full content coming soon — including the per-state rate-publishing schedule (which quarters land when).