Key takeaways
- Regular seller's permit holders file Form 850 in TAP, and the Commission says paper returns are no longer mailed.
- The Commission assigns monthly, quarterly, semiannual or annual filing, so read the schedule off the permit instead of guessing from sales volume.
- Due dates fall on the 20th, and a weekend or holiday moves the return and the payment to the next workday.
- A zero return is still required, and 12 months of $0 reported can lead to permit cancellation.
- Idaho local option taxes exist in 23 listed cities, and the Commission's page sends you to each city for details.
Where the return goes and what it covers
Sellers with a regular permit file and pay through TAP at tap.tax.idaho.gov. The Commission's Filing and Paying page says paper returns are no longer mailed. If a client needs a paper return, it can be printed from the Letters panel in TAP, and only the form preprinted with that client's period and account number may be used.
The return is Form 850, the Sales and Use Tax Return. The state sales tax rate and the use tax rate are both 6%. The forms page lists the Form 850 instructions as the 2025 edition, so open the instructions for the period you are filing before relying on a line description.
Idaho is an accrual state for sales tax. The Commission says tax is forwarded for the period of the sale even if the customer has not paid yet, so a December invoice paid in January belongs on the December return.
How filing frequency is assigned
The Commission assigns the schedule when the permit is set up: monthly, quarterly, semiannual or annual. Most retailers file monthly, and retailers who owe less than $750 in tax per quarter pay quarterly. Distributors and wholesalers with only a few sales can apply for semiannual or annual filing.
The rule that sits behind this, IDAPA 35.01.02.105, makes monthly the default and lets filers who owe $750 or less per quarter request quarterly or semiannual periods. It also lets the Commission require annual filing from a seller reporting less than $12,000 per year in taxable sales.
Decision rule: do not move a client to quarterly because their liability dropped under $750 a quarter. Check the filing frequency shown in TAP, and if the client wants a change, ask the Commission and get the new schedule confirmed before you stop filing monthly.
Due dates for 2026 and early 2027
Monthly returns are due by the 20th of the following month, so July tax is due August 20. Quarterly returns are due within 20 days after the quarter ends, semiannual returns by July 20 and January 20, and annual returns by January 20. If the 20th is a weekend or holiday, the return and the payment are due the next workday.
Applying that to the calendar: the October 2026 return is due Friday, November 20, 2026. The November return is due December 20, which is a Sunday, so it is due Monday, December 21, 2026. The December return, the fourth quarter return, and the annual return for 2026 are all due Wednesday, January 20, 2027. The first quarter of 2027 follows on April 20, 2027.
The weekend shifts are my application of the Commission's rule to the calendar, not dates printed on its page.
What goes on Form 850 and what stays off
Report all of the client's sales on Form 850, including sales at events. Leave off sales made through a registered marketplace facilitator or a short-term rental marketplace that already reports those sales to the state, because the Commission says not to report them.
Taxable price rules decide the most common reconciliation differences. Retailer coupons and retailer trade discounts reduce the taxable price. Prompt-payment discounts and manufacturer rebates do not, except motor vehicle rebates paid to the seller. Shipping charged to the buyer, installation labor and repair labor are not taxable if separately stated on the invoice, so a client who lumps them into one line price may be overpaying.
Exempt and resale sales need paper behind them. The Commission's certificate is Form ST-101, Sales Tax Resale or Exemption Certificate. Ask the client for the certificate for every customer who buys without tax, and match it to the customer name on the invoices.
Local option taxes
The Commission's city sales tax page lists 23 cities with local option sales taxes, among them Ketchum, Sun Valley, McCall, Sandpoint and Driggs, and tells readers to contact each city for questions. It does not give rates or say how a seller reports them.
Those taxes are voter-approved. The Commission says resort cities can tax anything subject to the state sales tax, but some limit the tax to lodging, alcohol by the drink and restaurant food, so the base differs from one city to the next. Some areas also have a separate auditorium district tax.
For a client with a location, or customers, in one of those cities, ask for the city name on the invoices and the point-of-sale tax setup, then confirm with the city which tax applies and how it is reported before the first return. Do not assume the 6% state rate is the whole tax.
Penalties, zero returns and large payments
A late return carries a penalty of 5% of the tax due for each month it is late, up to 25%. If the return is filed but the tax is not paid, the penalty is 0.5% of the tax due per month, up to 25%. The minimum penalty is $10, any part of a month counts as a full month, and there is no penalty if no tax is due. Interest runs from the original due date.
Example: a client has $48,000 of taxable September sales, which is $2,880 in tax at 6%. The return is filed and paid three days late. Using the filing penalty, the penalty is at least 5% of $2,880 comes to $144. The same return filed on time and paid three days late would use the 0.5% rate, about $14.40. The Commission's page does not say how the two combine on a return that is both late and unpaid, so budget for the higher figure.
A return is required every period for an active permit, even with no sales. Reporting $0 sales for 12 months in a row leads to permit cancellation, and a cancelled permit cannot be used to make sales or to buy goods for resale. Payments of $100,000 or more must go by ACH debit or ACH credit, or the state can charge interest and a $500 penalty.
Records to collect each period
Ask for the same items every period, with the period end as the deadline. That means the sales report from the point-of-sale or invoicing system showing gross sales, taxable sales, exempt sales and tax collected, plus the processor or marketplace reports that show which sales a facilitator already taxed.
Add the exemption certificates for any new tax-free customer, the invoice numbers behind any credit memo or return, and any purchases on which the client paid no sales tax and owes use tax. Self-assessed use tax goes on Form 850-U, which the Commission says must be paid by check or cash.
A request that asks for the same five items on the 5th of every month beats a fresh email each time. Usual can send a recurring monthly request with an upload field per item and a due date, and reminders go out until the files are in. Aim to have the sales report in hand before the 15th.
When a client crosses into filing
Idaho residents using the small seller exemption who exceed $5,000 in cumulative sales in a calendar year must start collecting tax immediately and apply for a permit within 30 days. For a new client, ask for year-to-date sales by month, not just the year total, so you can see the month the line was crossed.
Add the client to the filing calendar on the day the permit number arrives, because a late start is a common cause of a first penalty.