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Small Business Tax Deadline Calendar

Every tax deadline your business faces, with the amount beside each payment: estimated payments, the safe harbor they meet and the balance left for April.

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Pack of 10 files: 5 documents, 5 spreadsheets

Small Business Tax Deadline Calendar
  • Obligation SummaryDocument
  • Payment GuidanceDocument
  • The April Nobody Put on the CalendarDocument
  • Assumptions and What This Pack Does Not DoDocument
  • The Quarterly RoutineDocument
  • Deadline CalendarSpreadsheet
  • Estimated Payment CalculationSpreadsheet
  • Safe Harbour ComparisonSpreadsheet
  • Payment LogSpreadsheet
  • Underpayment ExposureSpreadsheet
RiverSmall Business Tax Deadline Calendar

Deadline Calendar

[Company] — tax year [YYYY]

One row per filing occurrence, not one per tax type, so a quarterly return appears four times with four dates. Every row carries the reason it applies to this entity, and every row that carries a payment carries an amount.

Due dateTax typeFormApplies because AmountSourceStatus
—Federal estimated income tax Period (a)No withholding on business income —Estimated Payment Calculation —
—Federal annual return Personal or entityEntity type —Safe Harbour Comparison —
—Payroll quarterlyQuarterly Employer of record— Payroll register—
—Payroll deposits Schedule changeLookback total against the threshold n/aObligation Summary —
—Federal unemploymentAnnual $1,500 of wages in a quarter, or an employee in 20 weeks— Payroll register—
—State estimated income tax State voucherResident state has an income tax fill inState return fill in
—Sales and use tax State returnWhat you sell is taxable where you sell it fill inSales register fill in
—Entity return, partnership or S corp Not applicableWould apply on an election n/a—Kept on the calendar
Balance due at filing—— Projected tax less what the floor requires— Safe Harbour Comparison—

Three parts of this calendar go beyond a list of due dates. The reason column makes the row auditable and stops a generic list carrying dates this business does not owe. The amount column refuses to be blank, because a blank reads as zero. And the last row is the balance the safe harbour leaves behind, which is a knowable number from the moment the payment strategy is chosen and the one that actually decides whether April is survivable.

How to keep track of small business tax deadlines

To keep track of small business tax deadlines, list every return and payment your business owes in one calendar, each with its due date and amount. For a sole proprietor, partner or S corporation shareholder, the core is four federal estimated tax payments, due April 15, June 15, September 15 and the following January 15. A good calendar also shows what each payment should be under the federal safe harbor rules, and the balance you'll still owe when you file.

The dates are public and the same for everyone. The amounts depend on your own return and books, and that's where the work is.

Hands holding a pen over a 2025 Form 1040, beside a calculator, a notebook, a laptop and a cup of coffee
Start with two lines on last year's return: total tax and adjusted gross income. Photo: Kelly Sikkema on Unsplash

List the tax deadlines your business has

Build the list from facts about your business. How it's taxed sets your return and its date, payroll adds employment returns, and taxable sales add state sales tax returns. The federal dates below follow the IRS's yearly tax calendar, Publication 5091.

Federal tax dates for a business on the calendar year

Business or obligationWhat's dueWhen
Sole proprietor or single-member LLCForm 1040 with Schedule C, and four estimated paymentsReturn April 15; payments April 15, June 15, September 15 and January 15
Partnership or multi-member LLCForm 1065, with a Schedule K-1 for each partnerMarch 15
S corporationForm 1120-S, with a Schedule K-1 for each shareholderMarch 15
C corporationForm 1120, and four estimated paymentsReturn April 15; payments April 15, June 15, September 15 and December 15
Employees on payrollForm 941 each quarter and Form 940 each yearForm 941 April 30, July 31, October 31 and January 31; Form 940 January 31

Partners and S corporation shareholders usually pay estimated tax on their share of the profit. A date that falls on a weekend or legal holiday moves to the next business day.

Your state adds its own dates, and its rules can differ. California's Franchise Tax Board, for example, requires 30% of the year's estimated tax by April 15, 40% by June 15, none in September and 30% by January 152. Licenses, annual reports and other non-tax filings belong on a small business compliance calendar.

Read two lines on last year's return

You generally avoid the federal underpayment penalty if your withholding and estimated payments reach the smaller of two amounts, often called the safe harbors. The IRS's estimated taxes page3 gives them as 90% of this year's tax or 100% of the tax on last year's return. Owing less than $1,000 after withholding and credits also keeps you clear.

Publication 505 adds a rule a growing business can cross without noticing. If last year's adjusted gross income (AGI) was over $150,000 ($75,000 if married filing separately), use 110% of last year's tax instead of 100%4. The publication takes AGI from line 11b of the 2025 Form 1040. Total tax is line 24, less any refundable credits and a few rarer items, and it includes self-employment tax.

One exception overrides all of this: if your total tax last year was zero, you don't need to pay estimated tax this year. That year must have covered 12 months, with you a US citizen or resident alien throughout.

Work out each estimated tax payment

  1. Project this year's tax

    Use profit from the months you've closed, forecast the rest from last year's same months, and work out both income tax and self-employment tax.

  2. Work out three floors

    90% of this year's projected tax, 100% of last year's total tax, and 110% of it if last year's AGI was over $150,000.

  3. Take the smaller one that applies

    Compare the 90% figure with whichever prior-year figure applies and take the smaller. Subtract any withholding you expect, then divide by four.

  4. Check what's already scheduled

    Set the result beside the payments you've arranged. If they are last year's tax divided by four and your floor is the 110% figure, every one is short.

ExampleOne contractor's payments, worked throughAn illustrative example written for this guide, using the template's made-up paving contractor.

Last year's return: total tax $41,820, adjusted gross income $172,860.

This year's projected tax: $79,171. 90% of that is $71,253.90, and 110% of last year's tax is $46,002. The requirement is the smaller, $46,002, or $11,500.50 a quarter.

Scheduled by the bookkeeper: $10,455 a quarter, which is last year's tax divided by four.

  • Short every quarter. Each payment is $1,045.50 too low, because AGI over $150,000 swaps 100% for 110%.
  • Still owed in April. Paying $46,002 on time avoids the penalty and still leaves $33,169 to pay with the return.

Plan for the balance due when you file

A safe harbor protects you from the penalty, not from the bill. Whatever your payments don't cover is due with the return, on April 15 for most owners. In the example that's $33,169, due just as the paving season starts, after three winter months of losses.

Paying 90% of this year's projection instead costs $25,251.90 more during the year and takes exactly that much off April's bill. The total is the same; only the timing changes. Pay the lower amount only if you'll leave the difference untouched, ideally in a separate account. Either way, enter the April balance in your small business cash flow forecast as a dated payment now.

Catch up at the next due date

The IRS figures the penalty separately for each due date. So you can owe it for an earlier due date even if you paid enough later5, and even if you're due a refund. It works like interest, at the federal short-term rate plus 3 percentage points. The IRS's quarterly interest rates6 put that at 7% for most of 2026, or about 19 cents a day for each $1,000 you're short.

Each payment goes to the oldest shortfall first, whichever period you mark it for. In an example in the same instructions, a $500 shortfall from April 15 is covered by a June 10 payment, so its penalty runs for 56 days. When you find a gap, add it to the next payment instead of waiting for the return.

If your income comes late in the year, consider the annualized income installment method. It bases each payment on income earned so far, so a slow start can mean lower early payments and higher later ones. Use it for one due date and you must use it for all four, filing Form 2210 with your return. In the example, a loss through March means nothing is due on April 15.

When to bring in a CPA or enrolled agent

This guide covers general US federal rules and isn't tax advice. Get help if you're changing how your business is taxed, earn income in several states, have already missed payments, or think a penalty waiver might apply.

Update the calendar before every due date

Two weeks before each due date, close last month's books and redo the projection. An expense and receipt organization template keeps receipts matched, so the close is quick. Check whether a different floor now applies, confirm that every payment cleared (your IRS online account shows your payment history), and settle on one amount. After you file each return, replace last year's two lines with the new ones.

Employers need one more yearly check. The IRS's employer guide, Publication 15, sets each year's deposit schedule from the four quarters ending the previous June 307. If the tax on those Forms 941 totals $50,000 or less, you deposit monthly. Above that, you deposit semiweekly, on a schedule tied to each payday. One extra seasonal crew can tip you over, so total it each July.

Before each due date

  • Last year's AGI and total tax come from the filed return
  • The projection uses books closed through last month
  • You know which floor applies, and why
  • Every earlier payment has cleared
  • This payment covers any earlier shortfall
  • April's balance is in your cash flow forecast

Each contractor you paid above the IRS reporting threshold needs a Form 1099-NEC every January, and a 1099 filing checklist tracks them. The template at the top of this page includes the full example, and Edit with AI opens it in River to build yours from your return and books.

How to use this template

Use the files as they are, or open them in River. River asks for last year's return, this year's profit and loss by month, payments made so far, payroll returns if you have staff, and any other household income. It tells you which safe harbor applies, works out each payment, shows the balance left for April and then fills in your calendar. A weekly check lists anything due within 30 days and any payment with no matching bank debit.

  1. Download it or open it in River

    Download the five Word documents and five CSV sheets free, or open the template in River and send your return.

  2. Send your return and books

    Share last year's return, this year's profit and loss by month, payments made so far, and payroll returns if you have staff.

  3. Get each payment and April's balance

    River names the safe harbor that applies, works out the amount for each due date, and shows what's left to pay when you file.

  4. Recheck before every due date

    Two weeks ahead, update the projection, confirm payments cleared and settle the amount. A weekly reminder flags what's due.

What's in the template

One contractor, three floors, and a $33,169 AprilThe Estimated Payment Calculation, the Safe Harbour Comparison, and the Underpayment Exposure sheet.
Small Business Tax Deadline Calendar
RiverThe three floors

Three floors, and the ten per cent nobody sees

Kestrel Pavement Services, invented. Sealcoating and line striping, single-member LLC filing jointly, four crews in season and two through the winter. Sealer will not lay below about ten degrees, so the season runs April through October and there is nothing to sell for five months.

LineItemAmountWhere it comes from
12026 Schedule C profit, projected $308,300.00Books to Aug 31, plus the season
2Self-employment tax $31,447.17Net earnings, wage base, surtax
5Taxable income $260,532.63Line 1 less half of line 2 less $32,200
7Total tax, projected 2026 $79,171.00Line 6 plus line 2
FloorAmountApplies?
90% of 2026 projected tax$71,253.90 Yes
100% of 2025 tax of $41,820$41,820.00 No. Prior-year AGI was $172,860
110% of 2025 tax$46,002.00 Yes
Required annual payment, the smaller $46,002.00Installment $11,500.50

Kestrel's bookkeeper set the estimates at last year's total tax divided by four, which is $10,455 a quarter. Four payments, four correct dates, a real figure off a filed return. Short by $1,045.50 every time, because the $150,000 AGI line switches the prior-year multiplier from a hundred to a hundred and ten and nothing announces it. The threshold is not indexed, so a growing business crosses it once and stays across it.

RiverWhat April costs

Four ways to play it, and the April each one leaves

A safe harbour is a minimum below which interest starts, not a settlement of the year. Every strategy has a second number, and a calendar only ever shows the date.

StrategyPer quarterPaid in-year Balance Apr 15PenaltyCash needed Jan 1 to Apr 15, before next year's estimates
Last year's tax over four$10,455.00 $41,820.00$37,351.00 $192.08$70,798.08
110% of last year, the binding floor $11,500.50$46,002.00 $33,169.00$0 $67,469.50
90% of this year's projection$17,813.48 $71,253.90$7,917.10 $0$48,530.56
100% of this year's projection$19,792.75 $79,171.00$0 $0$42,592.75
Jan 1 to Mar 31 trading result— —— —−$22,800.00

The middle two rows are the real choice, and it is a wash. Moving from the floor to the 90% figure costs $25,251.90 more during the season and removes exactly $25,251.90 from April. Identical totals. Only the timing moves. So it is not a tax question, it is a question about whether the money will still be there in April, which is a question about the owner. Kestrel has held a separate tax account untouched for three years, so the floor is right here and the held cash is free working capital.

RiverPer period

Each date stands alone, so the date is the answer

The charge is figured separately for every installment date at the federal short-term rate plus three percentage points. A January catch-up does not repair an April shortfall, and being owed a refund at filing does not either.

PeriodDueCum. requiredCum. paid Short byRuns untilDaysCharge
(a)Apr 15, 2026 $11,500.50$10,455.00 $1,045.50Jun 15, 2026 61$10.48
(b)Jun 15, 2026 $23,001.00$20,910.00 $2,091.00Sep 15, 2026 92$36.03
(c)Sep 15, 2026 $34,501.50$31,365.00 $3,136.50Jan 15, 2027 122$73.39
(d)Jan 15, 2027 $46,002.00$41,820.00 $4,182.00Apr 15, 2027 90$72.18
Do nothing—— —— —— $192.08
Top September up to $13,591.50— —— —Jun 15 and Sep 15 61 and 92$46.51

Each payment goes to the oldest shortfall first, so periods (a) and (b) stop in June and September anyway. Topping September up by the $3,136.50 cumulative shortfall, then paying January in full, clears the other two, taking $192.08 down to $46.51. That saves $145.57, which is 75.8% of the exposure, and the saving expires on September 15. Two hundred dollars is not a crisis, and the honest reading is that the interest was never the problem. The shortfall was a signal that the estimates came off the wrong number, and that wrong number was still running for two installments nobody had made yet.

RiverThe seasonal relief

A dead first quarter can require nothing at all

The annualised income installment method measures income cumulatively at four cutoffs, scales each figure to a full year, and takes a rising fraction of the tax on it. The cutoffs are the ends of March, May, August and December, and they are not calendar quarters.

PeriodCutoffCumulative profitFactor AnnualisedTax on thatApplicable % Cumulative required
(a)Mar 31 −$22,8004.0 −$91,200$0 22.5%$0
(b)May 31$45,600 2.4$109,440 $23,308.3845% $10,488.77
(c)Aug 31$246,200 1.5$369,300 $95,755.6367.5% $34,501.50
(d)Dec 31$308,300 1.0$308,300 $79,171.0090% $46,002.00

Kestrel loses $22,800 through March, so the annualised income is negative, the tax on it is nothing, and the required April installment is nothing, against $11,500.50 under the equal method. The relief reverses in period (c), where the annualised figure of $64,635.05 is capped at the regular cumulative and the installment becomes $24,012.73. The annual total is $46,002 either way. What changed is that $11,500.50 stays in the business from April to September, which for a contractor buying a season's sealer in April is worth more than the September inconvenience. Using it covers all four dates, needs closed books at four points in the year, and is claimed with the return.

  • Deadline Calendar sheetOne row per filing or payment, with why it applies, the amount, its source and status.
  • Estimated Payment Calculation sheetProjected profit to total tax, then the three safe harbor floors and the required installment.
  • Safe Harbour Comparison sheetFour ways to pay side by side, with each quarterly amount and the balance due at filing.
  • Payment Log sheetEach payment with its confirmation, total paid against the requirement, and whether you're short.
  • Underpayment Exposure sheetEach period's shortfall, days and penalty, a catch-up comparison, and the annualized method.
  • Obligation SummaryWhat the business owes, to whom and on what schedule, and which items hinge on a threshold.
  • Payment GuidanceWhat to pay on each date and why, plus the one fact that would change the advice.
  • The April Nobody Put on the CalendarThe worked example in full: a seasonal contractor's floors, shortfalls and April balance.
  • The Quarterly RoutineThe checks to run before each due date, after each payroll quarter and after you file.
  • Assumptions and What This Pack Does Not DoWhat the example simplifies, and what the template won't do, such as filing or computing state tax.

Common questions

What are the small business tax deadlines for the 2026 tax year?

For a calendar-year business, owners' 2026 estimated payments are due April 15, June 15 and September 15, 2026, and January 15, 2027. Partnership and S corporation returns for 2026 are due March 15, 2027, and individual and C corporation returns April 15, 2027. Employers file Form 941 by the last day of the month after each quarter.

How much should each quarterly estimated tax payment be?

Usually a quarter of the smaller of 90% of this year's tax or 100% of last year's total tax, after subtracting any withholding. If last year's adjusted gross income was over $150,000, use 110% of last year's tax instead. Paying that on time avoids the penalty, but any tax it leaves uncovered is still due with your return.

What happens if I miss an estimated tax payment?

You'll likely owe a penalty that works like interest: the IRS underpayment rate, 7% for most of 2026, on the amount you were short for each day it stays unpaid. Each due date is figured separately, so pay the gap as soon as you can. Usually the IRS calculates the penalty and mails you a bill.

Do S corporation owners and partners pay estimated tax?

Generally, yes, if they expect to owe $1,000 or more when they file their return. The IRS lists partners and S corporation shareholders, along with sole proprietors, among the individuals who usually pay it. Tax withheld from a salary you draw through payroll counts toward the requirement and reduces each payment.

Can I skip the January estimated tax payment?

Yes, if you file your 2026 return by January 31, 2027, and pay all the tax you owe with it. Publication 505 says the January 15 payment is then unnecessary. You can still owe a penalty if any of the first three payments was too small, figured up to the day you paid.

Is this small business tax deadline calendar free?

Yes. Download the five Word documents and five CSV sheets with no signup. They come filled in with a made-up paving contractor's year, so you can see how each sheet works before you replace the figures with yours. Edit with AI opens the same template in River.

What does Edit with AI do?

It opens the template in a free River workspace. River asks for last year's return, this year's monthly profit and loss, the payments you've made and any payroll returns. It names the safe harbor that applies, works out each payment and the balance left for April, then fills in your calendar. It doesn't file or pay anything, and it isn't tax advice.

Sources

  1. IRS. “Publication 509 (2026), Tax Calendars.” irs.gov (opens in a new tab)

  2. California Franchise Tax Board. “Estimated tax payments.” ftb.ca.gov (opens in a new tab)

  3. IRS. “Estimated taxes.” irs.gov (opens in a new tab)

  4. IRS. “Publication 505 (2026), Tax Withholding and Estimated Tax.” irs.gov (opens in a new tab)

  5. IRS. “Instructions for Form 2210 (2025).” irs.gov (opens in a new tab)

  6. IRS. “Quarterly interest rates.” irs.gov (opens in a new tab)

  7. IRS. “Publication 15 (2026), (Circular E), Employer’s Tax Guide.” irs.gov (opens in a new tab)

Written by

Chandler Supple

Co-founder & CEO, River

Chandler has spent the last six years working in AI, building tools for millions of users and Fortune 100 companies. In 2025, he co-founded River to build a new kind of operating system for AI agents.

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Reviewed by

Brian Joseff, Co-founder, River

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