Historical queries

Pass as_of=YYYY-MM-DD to retrieve the sales tax rate in effect on a specific date — useful for refunds, returns, audits, and rate recomputation after a customer dispute.

from datetime import date
from taxql import TaxQL

client = TaxQL(api_key="...")

# Q2 2026 rate (effective 2026-04-01 .. 2026-06-30)
q2 = client.lookup(state="wa", zip="98039", as_of=date(2026, 6, 1))

# Q3 2026 rate, even if today is still in Q2
q3 = client.lookup(state="wa", zip="98039", as_of=date(2026, 7, 15))

Supported states (carry effective-period history): TX, CA, FL, WA, NY, and all 24 SST states.

Snapshot-only states (return current rate regardless of as_of): NM, MO, IL, CO, LA, AL, AZ, AK. The DoR publishes only the currently-effective row; historical periods would require us to backfill rate publications by hand. Document your audit window accordingly.

When as_of predates the earliest loaded rate file for the state, the API falls back to the oldest available period and logs a warning internally; the response is returned but ops is alerted to the coverage gap.

Full content coming soon — see also Effective dates.