The 12 Biggest IRS And State Tax Deadlines Startups Miss (And What It Costs)

2025-11-21

If you run a startup long enough, you will miss a tax deadline. The goal is to avoid the expensive ones and fix mistakes fast.

This guide walks through twelve IRS and state deadlines that hit startups hardest, what it costs when you miss them, and how tools like Afternoon help you keep a clean calendar. It assumes a typical Delaware C corporation on a calendar year. This is general information, not legal or tax advice.

A quick calendar view

For a calendar year C corporation, the key dates often look like this:

January: W-2, 1099, and Form 940 deadlines
March: Delaware franchise tax for Delaware corporations
April: Form 1120 and first corporate estimated tax payment
Quarterly: Payroll Form 941, corporate estimated taxes, and many state sales tax returns
Year round: State payroll returns, California minimum tax, 83(b) elections, and foreign information forms like 5472

Let’s break that into twelve concrete deadlines.

1. Federal C corporation return (Form 1120)

What it is:

Form 1120, U.S. Corporation Income Tax Return is the main federal income tax return for C corporations.

Typical due date:

For a calendar year corporation, the return is due on the 15th day of the fourth month after year end (usually April 15).
You can often extend filing with Form 7004, but the extension does not extend the time to pay.
See IRS Publication 509, Tax Calendars for the official date grid.

What it costs if you miss it:

Failure to file penalty: generally 5 percent of the unpaid tax for each month or part of a month that the return is late, up to 25 percent.
Failure to pay penalty: generally 0.5 percent per month or part of a month, up to 25 percent.
Interest accrues on top of both; see Interest on underpayments.

How Afternoon helps:

Afternoon reads your books and projected tax, then surfaces your expected balance due before the filing date so you can pay on time and reduce penalties if you do need an extension.

2. Corporate estimated tax payments

What it is:

Corporations often need to pay income tax during the year, not just at filing. These are corporate estimated tax payments.

Typical due dates:

For calendar year corporations, estimated tax installments are due on the 15th day of the 4th, 6th, 9th, and 12th months of the year (usually April 15, June 15, September 15, and December 15).
See Instructions for Form 1120 and Publication 542, Corporations for details.

What it costs if you miss it:

The IRS can charge an underpayment of estimated tax penalty if you do not pay enough on time.

How Afternoon helps:

Afternoon compares your year to date tax to prior years and your forecast, then flags when you are likely to owe estimates and adds those dates to your compliance checklist.

3. Quarterly payroll tax returns (Form 941)

What it is:

Form 941 is the quarterly federal return for income tax withholding, Social Security, and Medicare taxes on wages.

Typical due dates:

For most employers, Form 941 is due by the last day of the month after the quarter ends: April 30, July 31, October 31, and January 31.
See Publication 15, Employer’s Tax Guide and the Employment tax due dates page.

What it costs if you miss it:

Missing returns or deposits can trigger failure to file, failure to pay, and failure to deposit penalties, plus interest.

How Afternoon helps:

Afternoon pulls payroll data, checks whether filings match the wage and tax amounts in your books, and highlights missing quarters before the IRS notice shows up.

4. FUTA annual return (Form 940)

What it is:

Form 940, Employer’s Annual Federal Unemployment (FUTA) Tax Return reports federal unemployment tax.

Typical due date:

For a calendar year, Form 940 is due January 31 of the following year.
If all FUTA deposits were made on time, you usually have until February 10.

What it costs if you miss it:

Late filing and payment bring the same family of penalties: failure to file, failure to pay, and failure to deposit, plus interest. See Topic No. 653 – IRS notices, penalties and interest.

How Afternoon helps:

Afternoon links payroll data and FUTA exposure so your accountant can see, in one place, what should be on Form 940 and whether it has been filed.

What it is:

Form W-2 reports wages and tax withholding for each employee.
Form W-3 summarizes all W-2s for the Social Security Administration (SSA).

Typical due date:

W-2s must be furnished to employees and filed with the SSA by January 31.
See the SSA’s Employer W-2 Filing Instructions & Information.

What it costs if you miss it:

Late or incorrect W-2s can trigger information return penalties under sections 6721 and 6722. The IRS lists the dollar amounts per form and caps per year on that page.

How Afternoon helps:

Afternoon cross checks W-2 totals against your payroll and books so you can catch mismatches before filing and avoid reissued forms and penalties.

6. 1099-NEC and other 1099s for contractors and vendors

What it is:

Form 1099-NEC reports nonemployee compensation, such as payments to many contractors.
Other forms in the 1099 series cover interest, rents, and other payments.

Typical due dates:

For Form 1099-NEC, you generally must file with the IRS and furnish statements to recipients by January 31.
The official dates are in the 1099-NEC instructions linked above.

What it costs if you miss it:

Information return penalties in Information Return Penalties apply here too, and they stack if you miss multiple forms.

How Afternoon helps:

Afternoon tags contractor and vendor payments in your books so you can pull a clean list of 1099 candidates and avoid guessing in January.

7. Delaware franchise tax and annual report

What it is:

If you are a Delaware corporation, you must file an annual report and pay Delaware franchise tax, even if you have no Delaware operations.
See the state’s Franchise Tax FAQs.

Typical due date:

Delaware states that franchise tax and annual reports are due no later than March 1 each year for domestic corporations.

What it costs if you miss it:

Delaware notes a 200 dollar late filing penalty plus 1.5 percent interest per month on the unpaid tax and penalty. Details are on the Delaware Division of Corporations.

How Afternoon helps:

Afternoon tracks your legal entity data and reminds you when state level annual filings like Delaware franchise tax are coming up, alongside federal deadlines.

8. California minimum franchise or annual tax

What it is:

Many entities that do business in California owe a minimum annual tax (often 800 dollars), even if they have no income.
See the California Franchise Tax Board’s Business Entities pages and the FAQ on the annual tax for limited liability companies.

Typical due date:

The annual tax is generally due by the fifteenth day of the fourth month of the taxable year for many entities, with special rules for first year entities.

What it costs if you miss it:

Missing California payments can lead to penalties, interest, and suspension of your entity’s good standing. The FTB site outlines these consequences in its business entity guidance.

How Afternoon helps:

Afternoon can tag your California presence from payroll, sales, or registrations, then note that you likely have a recurring state level tax obligation, even if your federal income is still low.

9. State sales tax filings

What it is:

If your product is taxable in a state and you have registered for sales tax, you must file returns and remit tax, often monthly or quarterly.

Typical due dates:

Each state’s department of revenue sets its own schedule. Many use monthly returns due around the 20th or end of the following month.
The IRS does not control state sales tax, but the Small Business and Self-Employed Tax Center is a good hub with links to state agencies.

What it costs if you miss it:

States can assess late filing penalties, late payment penalties, and interest.
Localities can add their own penalties where local tax applies.

How Afternoon helps:

Afternoon’s sales tax engine maps your revenue by state, tracks where you are registered, and builds a due date calendar by jurisdiction so you do not rely on a generic reminder.

10. State payroll returns and deposits

What it is:

On top of federal payroll filings, states have their own withholding returns, unemployment returns, and deposit schedules.

Typical due dates:

Dates vary, but many states require quarterly wage reports that align with Form 941 and monthly or semiweekly deposits for withheld tax.
The IRS employment tax due dates page is a useful model for how these schedules are structured.

What it costs if you miss it:

Failure to deposit or file state payroll taxes can lead to state level penalties similar to federal employment tax penalties, plus interest.

How Afternoon helps:

Afternoon reads your payroll runs and flags where wages and taxes are being paid so your accountant can confirm that the right state accounts and due dates are set up.

11. 83(b) elections for founder and employee stock

What it is:

An 83(b) election lets someone who receives restricted stock choose to pay tax on the current value upfront instead of as the stock vests over time.

Typical due date:

The election must be filed with the IRS no later than 30 days after the date the stock is transferred. There are no extensions.
See the sample 83(b) election statement.

What it costs if you miss it:

If you do not file within 30 days, the election is not valid. The default rule applies, which usually means ordinary income each time stock vests, often at much higher valuations later.

How Afternoon helps:

Afternoon does not file elections, but your tax and legal partners can store 83(b) status alongside cap table data and use our reporting to plan around the eventual tax impact.

12. Foreign ownership information returns (Form 5472 and friends)

What it is:

Form 5472 is an information return for certain 25-percent foreign-owned U.S. corporations and foreign corporations engaged in a U.S. trade or business.
Other forms such as Form 5471 apply when U.S. persons own foreign corporations.

Typical due date:

Form 5472 is generally due with the related corporation income tax return (for example, Form 1120), and follows the same extension rules when you file Form 7004.

What it costs if you miss it:

The Form 5472 instructions describe a 25,000 dollar penalty for failure to file or maintain required records, with additional 25,000 dollar penalties if the failure continues after notice.

How Afternoon helps:

Afternoon’s onboarding process collects ownership and foreign activity details so your tax team can see early if forms like 5472 or 5471 might apply and plan filings with the main return.

A simple way to keep this under control

You do not need to memorize every rule. You do need a single place where:

Your entity structure, payroll footprint, and state registrations are accurate
Your accounting system is clean and up to date
Your tax calendar pulls directly from that data rather than a static checklist

Afternoon’s bookkeeping, sales tax, and tax review workflows are built to sit on top of your books and bank data, then surface deadlines alongside the dollars. That way when you look at your monthly review, you see not just what happened last month, but what the IRS and the states expect from you next.