The Short Tax Year: How to File a Stub Return Without Overpaying

Your business earned $90,000 in six months — and the IRS wants to tax you as though you earned $180,000. That is not a penalty and not a mistake. When your tax year covers fewer than 12 months, the law forces you to annualize: scale the stub period up to a full year, compute the tax on the inflated number, then scale the tax back down. Do it wrong and you hand the government an interest-free loan; skip the relief procedure and you may never get the overpayment back.

A short tax year shows up more often than owners expect: you incorporate in July, shut a business down in October, or switch from a calendar year to a fiscal year. Each situation gets its own filing and tax-computation rules, and the most expensive error is treating them all the same. Here is how each case works and where the traps are.

What Counts as a Short Tax Year​

A short tax year is any tax year shorter than 12 months. Section 443 of the Internal Revenue Code recognizes exactly two situations that create one:

1. You change your accounting period (with IRS approval). The short period runs from the day after your old year closed through the day before your new year begins.
2. You were not in existence for the whole year. A corporation formed on July 1 files a first return covering July 1 through December 31. A calendar-year corporation that dissolves on July 23 files a final return covering January 1 through July 23.

Two more situations produce short periods through their own rules: an S corporation whose election terminates mid-year splits that year into an S short year and a C short year, and a decedent's final return covers January 1 through the date of death.

The critical point — the one that determines everything else — is that the tax is figured differently for each situation. Annualization applies only to short years caused by a change of accounting period. If your short year exists because the business started or stopped, you generally figure the tax the normal way, with no annualizing at all.

Case 1: You Started or Closed Mid-Year (No Annualization)​

This is the common case and the simplest. IRS Publication 538 states the rule plainly: when the entity was not in existence for the entire year, the filing requirements and the tax computation are generally the same as for a full 12-month year ending on the last day of the short year.

What that means in practice:

• A July startup files a July–December return and computes tax on exactly what it earned in those months. No scaling up, no scaling down.
• A dissolved business files a January-to-dissolution-date final return the same way. Mark it as the final return, close the EIN account, and file final employment tax returns if you had payroll.
• A decedent's final return may be filed and the tax paid as though the person had lived through the entire year — including claiming the full standard deduction. The return is due by the usual April deadline of the following year.

New owners sometimes hear about "annualizing" and apply it to a startup stub year, inflating their income for no reason. If nobody changed an accounting period, annualization does not enter the picture.

Case 2: You Changed Your Accounting Period (Annualization Required)​

If the IRS approves a change in your tax year — say, from a calendar year to a fiscal year ending June 30 — you must file a short-period return for the gap (January 1 through June 30 in that example) and figure the tax under the Section 443 general rule: annualize.

Why the law makes you annualize​

Without annualization, a taxpayer could change tax years repeatedly to run the same income through the lowest brackets again and again. Annualizing neutralizes the maneuver: your stub-period income is projected to a 12-month equivalent, taxed at the rates that equivalent would face, and the resulting tax is then prorated back to the stub. You pay roughly what you would have paid had you earned at that pace all year.

The individual computation, step by step​

Publication 538 gives the mechanical recipe for individuals:

1. Start with your adjusted gross income for the short period and subtract your actual itemized deductions for the short period. You must itemize — the standard deduction is not available on this return.
2. Subtract a prorated personal-exemption amount: the exemption figure times the months in the short period, divided by 12. (The exemption amount has been zero since 2018, so this step currently changes nothing, but the statute still requires it.)
3. The result is your modified taxable income.
4. Annualize it: multiply by 12 and divide by the number of months in the short period.
5. Figure the tax on that annualized income using the regular rate schedules.
6. Prorate the tax back down: multiply by the months in the short period and divide by 12. That is your short-year tax.

A concrete example: your short period is six months and your modified taxable income is $60,000. Annualized income is $120,000 ($60,000 × 12 ÷ 6). You compute the tax on $120,000 from the rate schedule, then cut that tax figure in half. If your income had instead been bunched — say, nearly all $60,000 earned in two of the six months — the annualized figure still assumes the six-month pace held all year, which is exactly why the relief procedure below exists.

Three adjustments people miss​

• Self-employment tax is not annualized. It is figured on your actual self-employment income for the short period. Only the income tax goes through the annualization machine.
• Withheld income tax is credited on a calendar-year basis. The amount withheld during a calendar year counts toward the tax year that began in that calendar year, regardless of where your new fiscal year falls.
• Alternative minimum tax gets its own annualization. Annualize the alternative minimum taxable income, apply the AMT rates, then prorate back — the same up-and-down shape as the regular computation.

The Relief Procedure: Getting the Overpayment Back​

Annualization assumes your income arrived evenly. When it did not — a retailer whose short period covers only the holiday season, a contractor paid on one big milestone — the general rule overstates the tax. Section 443(b)(2) provides a relief procedure that can produce a lower number.

The mechanics: after the short year, you establish what your taxable income was for the 12-month period beginning on the first day of the short period, computed as though that 12-month stretch were a tax year. The short-period tax is then recomputed two ways — one ratio-based method tying the short-period tax to the 12-month tax, and one straightforward tax-on-actual-short-period-income method — and your liability drops to the greater of the two, if that is below the general-rule figure.

Two procedural catches matter:

• You file first, claim later. You compute the tax under the general rule and file the short-period return without the relief. The relief comes afterward as a claim for credit or refund.
• There is a deadline. The application for relief must be filed no later than the due date (including extensions) of the return for the first tax year ending on or after the day that is 12 months after the short period began. Miss it and the general-rule figure stands.

If your short-period income was lumpy, calendar this deadline the day you file the stub return. It is the difference between a refund and a donation.

Depreciation in a Short Year: Tables Out, Conventions In​

Fixed assets get their own set of short-year rules, and they cut in both directions:

• Regular MACRS depreciation must be prorated. The published MACRS percentage tables assume a 12-month year, so you cannot read a rate off the table for a stub period. Instead you apply the property's convention (half-year, mid-quarter, or mid-month) on a month-counted basis — Publication 946 works through each convention's short-year math.
• Section 179 is not prorated. The amount you elect to expense is unaffected by placing property in service during a short tax year. Buy qualifying equipment in a six-month stub year and you may expense the full cost, subject to the normal dollar and taxable-income limits.
• Bonus depreciation is not prorated either. Property placed in service in a short year qualifies for the full special allowance percentage in effect for that year.
• Luxury-vehicle caps need a short-year adjustment. The first-year dollar limits on passenger automobiles assume a full year, so check the current revenue procedure's table notes before claiming the full cap on a stub-period vehicle.

The planning takeaway: in a short year, expensing provisions (Section 179, bonus) deliver a full year's benefit against a partial year's income, while MACRS dribbles out month by month. Model both before you decide how to write off a major purchase.

The Estimated-Tax Trap Nobody Warns About​

Many owners rely on the prior-year safe harbor — pay 100% of last year's tax (110% at higher incomes) and skip underpayment penalties. That harbor vanishes when the prior year was short: the statute requires the preceding taxable year to have been a full 12 months. A business whose first return covered seven months has no prior-year figure to anchor to, and must instead hit 90% of the current year's tax to stay penalty-free.

The same logic bites in reverse. If your current year is the short one, your required quarterly installments are computed against the short year's annualized liability, and the calendar-year withholding credit rule above decides which payments count where. When either side of the comparison is a stub, have your preparer recompute the estimates from scratch instead of copying last year's vouchers.

Deadlines and Paperwork​

• The short-period return is due as though the stub were a full year ending on its last day. A calendar-year C corporation whose short period ends June 30 faces the same relative deadline as a fiscal year ending June 30 — the 15th day of the fourth month after the close, with extension available on Form 7004. Individuals use the usual individual deadlines and Form 4868.
• Form 1128 requests IRS approval to change your tax year. A ruling request must be filed by the 15th day of the second calendar month after the short period closes. If you qualify for an automatic change, no user fee is required — you attach Form 1128 to your timely filed short-period return instead.
• Closed or converted entities have extra filings. A dissolving corporation checks the final-return box and files final payroll returns; an S corporation whose election terminates mid-year splits the year into S and C short years with income allocated per share per day (or, if all affected shareholders consent, an interim closing of the books).

Mistakes That Cost Real Money​

1. Annualizing a startup or shutdown year. The most common error, and it always inflates the bill. No change of accounting period, no annualization.
2. Claiming the standard deduction on a change-of-period stub. Individuals must itemize that return. Software sometimes defaults to the standard deduction — override it.
3. Using MACRS tables for the stub. The percentages assume 12 months. Compute convention-based depreciation month by month, or let Section 179 do the heavy lifting instead.
4. Copying last year's estimated payments. The prior-year safe harbor needs a 12-month prior year. Recompute.
5. Forgetting the relief-procedure deadline. The refund claim has its own due date a year out. Diary it.
6. Filing the year-change return without Form 1128. An unapproved change is an invalid change, and the IRS can recompute everything on your old year.

Closing the Books on a Stub Period​

A short tax year is really two disciplines: the tax computation above, and a clean stub-period close in your own books. Cut off revenue and expenses on the exact boundary date, reconcile every balance-sheet account as of that day, and keep the short-period trial balance separate from the new year's opening entries — especially around a year change, where one misdated invoice lands in the wrong return. Depreciation schedules need a stub-year column showing the prorated MACRS, the full Section 179, and the convention math, so next year's return picks up the right remaining basis.

Keep Your Stub-Year Records Audit-Ready​

Short years draw attention precisely because the numbers look unusual — half a year's revenue, a full Section 179 deduction, a refund claim filed a year later. Clear records are what make all of it defensible. Beancount.io provides plain-text accounting that gives you complete transparency and control over your financial data — no black boxes, no vendor lock-in. Get started for free and see why developers and finance professionals are switching to plain-text accounting.