Key takeaways
- The frequency comes from remittances for the 12 months ending October 31, and the thresholds are per quarter.
- Monthly returns are due the last day of the following month, early monthly returns on the 20th, and annual returns on January 31.
- Milwaukee County is 0.9% and the city of Milwaukee adds 2%, so a sale inside the city carries a 7.9% combined rate.
- Every active account files, including zero returns, and an extension does not stop interest on unpaid tax.
Who files and what the account looks like
A business that holds a Wisconsin seller's permit files a sales and use tax return, and the Department of Revenue collects it through My Tax Account. The return is Form ST-12 and sits under the Sales and Use Tax account, which is separate from the client's income tax filing.
Log in, choose File/Pay/View Returns for the Sales and Use Tax account, and then choose File Now for the period. If the portal lists more than one Sales and Use Tax account for the client, each one needs its own return.
Every active account files, even when there were no sales. The Department's annual filer page says all active accounts must file even if zero tax is due, so a dormant account still needs a zero return for each period it is assigned.
Set the filing frequency from the last 12 months
The Department sets each seller's filing frequency from remittances for the 12-month period ending October 31. The thresholds are per quarter. Early monthly is $3,601 or more per quarter, monthly is $1,201 to $3,600 per quarter, and quarterly is $601 to $1,200 per quarter. Annual is $600 per year or less.
For calendar-year filers, a change in frequency is first effective for periods beginning January 1. So the 12 months ending October 31, 2026 set the frequency for 2027 periods, and this is the window to check before the year closes.
Pull the client's sales tax remittances for November 2025 through October 2026 from the client's records or the portal's filing history, group them by quarter, and compare each quarter to the bands above. Confirm the frequency the portal shows for the account before the first period of 2027, because the due dates follow that assigned frequency.
2026 periods and due dates
The Department's FAQ says returns are due by the last day of the month following the end of the reporting period. Early monthly filers are the exception and file by the 20th of the following month. Annual returns are due January 31. If the regular due date falls on a weekend or legal holiday, it moves to the business day immediately after.
Worked dates for 2026 periods: the October 2026 monthly return is due Monday, November 30, 2026. The November 2026 monthly return is due Thursday, December 31, 2026. An early monthly filer's October 2026 return is due Friday, November 20, 2026.
The December 2026 monthly return, the fourth quarter 2026 return and the 2026 annual return all fall on January 31, 2027. That date is a Sunday, so the due date is Monday, February 1, 2027. Check the due date the portal shows for each period.
Enter the return and submit before the batch
Enter the period's sales and tax in the return, check the totals against the sales report, and submit. For a period with no activity, answer Yes to “Do you plan to report zero on every line?” and submit. Answer No if the period has any reportable amount, and complete the required fields.
The Department's page says pending submissions are sent to the Department each business day at 4:00 p.m. (CST). Submit the return by the business day before the due date instead of on it. A return finished after 4:00 p.m. on the due date may not reach the Department until the next batch, which can fall after the deadline.
Payments are pulled at the same time as the return. The portal lets the filer cancel a payment until 4 PM CST on the day it is submitted, so a payment that was entered by mistake can be stopped before the pull.
Extensions and interest
Use Request Extension to File in the Sales and Use Tax account, enter the filing period, and submit. The Department says you may request a 30-day extension to file business tax returns, and that the request must be made on or before the filing period due date. The Department may also grant one additional month from the original due date.
An extension covers the filing, not the payment. If tax is not paid by the original due date, it accrues 1% interest per month during the extension period and 1.5% interest per month after that. On $2,400 of tax paid one month late, the 1% interest is $24.
Calendar the extension request for a week before the due date. A request made after the due date does not meet the rule, so the return is late.
The 5% state rate, the county tax and the Milwaukee rates
The Wisconsin sales tax is a 5% tax on the sales price. A county may add a 0.5% county tax, and the Department says 70 counties have adopted it. The combined rate depends on the location of the sale, so the rate chart on the Department's site is the source for each county and city, not a single state table.
Milwaukee County's rate rose from 0.5% to 0.9% effective January 1, 2024. The city of Milwaukee adds a 2% city tax effective the same date. Inside the city, the combined rate is 7.9%. In the rest of Milwaukee County it is 5.9%.
Worked example: a client in the city of Milwaukee with $40,000 of taxable October 2026 sales owes $2,000 state tax (5%), $360 county tax (0.9%) and $800 city tax (2%), for $3,160 on that period.
Rate changes that affect 2025 and earlier periods
Racine County imposes a 0.5% county sales and use tax effective April 1, 2025, and Manitowoc County imposes one effective January 1, 2025. A sale made before those dates is not taxed at those county rates, so a 2024 amended return cannot pick up a county rate that started later.
Milwaukee County was 0.5% before January 1, 2024. An amended return for a 2023 period or earlier uses 0.5% for Milwaukee County and does not carry the 0.9% rate back.
The rate table in the sales system should carry an effective date for each county and city change. A table that stores only the current rate applies today's rates to older periods whenever an amended return is prepared.
Stadium taxes do not belong on 2026 returns
The baseball park district tax was a local tax under subchapter III of chapter 229 of the Wisconsin statutes. Under 2023 Wisconsin Act 40, section 14, retailers and the Department may not collect it after the last day of the fiscal quarter in which the district certifies to the Department, or after August 31, 2020, whichever is earlier.
A 2026 return should carry no stadium tax line. If a client's old rate table or software still adds a stadium rate, remove it before the next period and check the Department's rate chart.
Some third-party guides still list older special district taxes. Do not carry a stadium or special district rate into a 2026 table without a Department source for it.
Failure modes and fixes
A city sale charged at the county rate. A sale inside the city of Milwaukee charged at 5.9% instead of 7.9% under-collects 2 percentage points on every taxable sale. Fix it in the rate table by location, then check each January that the table matches the Department's chart.
A zero return skipped for an inactive account. Fix it by calendaring a zero return for every active account in every period, including the annual return in January.
A frequency that does not match the account. A client who files monthly on a quarterly account has returns that do not match the due dates. Fix it by checking the assigned frequency in the portal before the year starts and after any change in remittances.