Sales Tax API

https://api.api-ninjas.com/v1/salestax

Returns one or more sales tax breakdowns by ZIP code according to the specified parameters. Each breakdown includes the state sales tax (if any), county sales tax (if any), city sales tax (if any), and any additional special sales taxes. All tax values are presented in decimals (e.g. 0.1 means 10% tax).

https://api.api-ninjas.com/v1/salestaxnexus

Returns US sales tax economic nexus thresholds, and optionally determines whether a seller has crossed them. Call it with no sales figures to use it as a reference lookup of each state's rules, or supply your sales figures to get a determination. Omit state to evaluate all 50 states and DC in a single request.

Every nexus or no_nexus answer is provable from the figures you supply. Where your inputs cannot settle the question, the endpoint returns indeterminate together with a required_input array naming exactly which parameter would resolve it, rather than guessing. This matters because states measure different quantities: taxable sales are a subset of retail sales, which are a subset of gross sales, so Florida (which measures taxable sales) and Michigan (which measures gross sales including exempt ones) can reach opposite conclusions on the same seller.

This endpoint evaluates economic nexus only. Physical presence — inventory, employees, offices, contractors, trade shows — can create nexus at any sales volume and is not considered. It is reference data, not tax advice.

This endpoint is available to premium subscribers only. Requests on the free tier return an error.

https://api.api-ninjas.com/v1/salestaxholidays

Returns US sales tax holidays — the “tax free weekend” periods when states exempt certain purchases — with the eligible item categories and price caps for each. Omit state for a nationwide list of every holiday in a given year.

Start and end values are timezone-aware timestamps, not plain dates, because these holidays begin and end at specific local times. Alabama's, for example, runs from 12:01am on the first day to midnight on the last. A checkout integration that compares dates alone gets both boundaries wrong.

Price caps are almost always per item, not per transaction. A $150 basket of three $50 shirts qualifies under a $100 cap; a single $150 coat does not. Read cap_basis rather than assuming.

Where a state lets each city or county opt in or out, the endpoint returns exempt: null with determination: "indeterminate" and a required_input array naming what would resolve it, rather than a flat true that would be wrong for roughly half the localities in that state. An unrecognised category returns not_addressed, never exempt.

Asking for a year a state has not yet published returns an empty result set with a coverage note — not an error, and not last year's dates silently reused.

This is reference data, not tax advice.

https://api.api-ninjas.com/v1/salestaxfiling

Returns sales tax filing frequencies and due dates for 47 US jurisdictions. Supply a year to get the full calendar for a frequency; supply annual_liability to have the state's own rules assign the frequency.

Calendars are generated from each state's published rules, never stored. A hand-entered table of 47 states × 12 months rots the moment a state moves a date, and the rot is invisible until a customer files late.

This handles what a “due on the 20th” assumption gets wrong. Due days run from the 15th (Maine) to the last day of the month (California, Connecticut, Missouri, Utah, Wyoming). New York's quarters end February, May, August and November. Massachusetts is 30 days after the period, so its January return falls on March 2, not February 28.

Weekend and holiday rollover is applied against the federal calendar, a state one, or both, and the result carries due_date_adjusted plus the original statutory_due_date so you can see that the date moved and why. Where a state requires an electronic payment to be initiated before the nominal due date (Florida), efile_initiate_by gives that earlier date.

Prepayment regimes are included, in the four distinct placements states actually use — California and New Jersey cover one month and pay the next; Pennsylvania, Michigan, Ohio and seven others fall due inside the month being covered, before the period even closes. Omitting these gets the answer wrong for exactly the high-volume filers who need it.

Where a state grants a filing frequency by written approval or departmental notice rather than by a published dollar threshold — Georgia, Idaho, New Mexico, Oklahoma, South Carolina, Virginia and others — the response is indeterminate rather than a guess. Telling a Georgia seller “quarterly” when they are monthly-until-approved means filing late.

Every jurisdiction carries coverage_level, and any field a state does not publish is listed in unpublished with an unpublished_reason explaining why. Every frequency tier carries a statute_cite and source_url.

State-level filing regimes only. Colorado home-rule cities, Louisiana parishes, Alabama's non-state-administered localities and Alaska's ARSSTC jurisdictions each file separately and are out of scope.

This is reference data, not tax advice.