Estimated Taxes

Estimated taxes are quarterly payments an individual makes directly to the IRS on income that is not subject to withholding: self-employment earnings, investment income, rents, retirement distributions taken without withholding, taxable Social Security, prize money, and gains on a sale. Internal Revenue Service Publication 505 states the underlying principle in its opening lines: the federal income tax is a pay-as-you-go tax, so you must pay it as you earn or receive income during the year, and there are exactly two ways to do that, withholding and estimated tax. The payment voucher is Form 1040-ES, "Estimated Tax for Individuals."

The consequence of underpaying is set by section 6654, which is titled "Failure by individual to pay estimated income tax" and which imposes an "addition to the tax" rather than interest or a penalty in the ordinary sense. It is computed by applying the federal underpayment rate under section 6621 to the amount of each underpayment for the period it was outstanding, so it behaves like interest, but it is not deductible and paying the full balance in April does not remove it. Two names for the same thing are worth reconciling: everyone calls these "quarterly taxes," and the statute never uses the word quarter, because the four periods are of unequal length.

Who actually needs to do this. Anyone whose withholding will not cover enough of the year's tax, which in practice means the self-employed, retirees living on portfolio or distribution income, partners and S corporation shareholders taxed on business profit they did not receive as wages, landlords, and employees with substantial income on the side. An employee is not obliged to use estimated payments at all: increasing withholding on the W-4 is an alternative route to the same requirement, and often a better one for the reason below.

What the requirement actually is. Section 6654(d)(1)(A) sets each installment at 25% of the "required annual payment," and (d)(1)(B) defines that as the lesser of 90% of the tax shown on this year's return or 100% of the tax shown on last year's. Under (d)(1)(C) the prior-year figure becomes 110% if the adjusted gross income on last year's return exceeded $150,000, or $75,000 for a married individual filing separately. Both of those dollar amounts are statutory and have never been indexed. The prior-year test is unavailable if the prior year was not a full 12 months or if no return was filed for it.

Why the prior-year figure is the one to build a plan on. It is knowable in advance and completely immune to how the current year turns out. A freelancer whose income doubles, or a retiree who realizes an unexpected capital gain, has still satisfied section 6654 if the installments added up to last year's tax (or 110% of it). The remaining balance is then simply due in April with nothing added. That is what makes a volatile income manageable, and it is the reason the 90%-of-this-year test is usually the fallback rather than the target.

The single most useful mechanic on either this page or its withholding counterpart. Section 6654(g)(1) provides that the credit for tax withheld "shall be deemed a payment of estimated tax, and an equal part of such amount shall be deemed paid on each due date for such taxable year, unless the taxpayer establishes the dates on which all amounts were actually withheld." Withholding is therefore spread backwards across all four installments by default, and an estimated payment is credited on the date it is made. So a shortfall discovered in November can be cured by raising withholding on a paycheck or a year-end bonus, which is treated as though a quarter of it had arrived in April, while writing a larger check with the January installment cannot reach the earlier periods at all. Subsection (g)(2) lets you apply that even-spreading separately to wage withholding and to other withheld amounts.

The lever for lumpy income is the annualized method. The default assumes income arrives in four equal blocks, which punishes anyone whose year is back-loaded: a consultant paid in December, or an investor who sells in the fourth quarter, is treated as having underpaid three installments they had no way to anticipate. Section 6654(d)(2) allows each installment to be computed on income actually received through that point, annualized, at applicable percentages of 22.5%, 45%, 67.5% and 90%. It is filed on Form 2210 and it is more work, but it is the correct answer for genuinely uneven income. Note the recapture rule: an installment reduced this way increases the next one.

The exceptions that stop the section from applying. Section 6654(e)(1) disapplies the addition entirely if the year's tax, reduced by withholding, is less than $1,000, and (e)(2) disapplies it if the prior year was a full 12 months in which you had no tax liability at all and you were a US citizen or resident throughout it, which is the practical rule for a first year of self-employment following a year with no tax. Under (e)(3)(B) the IRS may waive the addition for someone who retired after reaching age 62 or became disabled, where the underpayment was for reasonable cause, and (e)(3)(A) allows a waiver for casualty, disaster or other unusual circumstances. Subsection (h) is a narrow but useful escape at the end of the year: filing the return and paying the balance in full on or before January 31 removes any addition attributable to the fourth installment. Farmers and fishermen get their own regime under subsection (i), with a single installment due January 15, a 66 2/3% test in place of 90%, and March 1 in place of January 31.

The mechanics, in order.

1. Decide which safe harbor you are aiming at. Look up the total tax on last year's return. If the adjusted gross income on that return was over $150,000, multiply it by 110%. That figure divided by four is an installment amount that cannot be wrong.

2. Subtract expected withholding. Any withholding from a job, a pension or a retirement distribution counts toward the same requirement, so only the remainder needs to arrive as estimated payments.

3. Pay by the four dates, April 15, June 15, September 15 and January 15 of the following year, using Form 1040-ES or an electronic payment. Missing a single date starts the clock on that installment alone.

4. Reconcile in April. The installments were only ever an approximation of the year's real tax; the return computes the actual figure and you pay or reclaim the difference.

A hypothetical example. Rafael's total tax last year was $28,000 and his adjusted gross income on that return was $120,000, which is under the $150,000 threshold, so his prior-year safe harbor is 100% of $28,000. He expects $4,000 of withholding from a part-time teaching job this year, so he needs $24,000 from estimated payments, which is $6,000 on each of the four dates. In November a client pays an unexpectedly large invoice and his actual tax for the year comes to $41,000. Because he paid in $28,000 through a combination of withholding and installments, he has met the prior-year safe harbor, so no addition to tax applies. He owes the remaining $13,000 with his return in April and nothing more.

Change one fact and the picture changes. Had Rafael's prior-year adjusted gross income been $160,000 instead, his target would have been 110% of $28,000, or $30,800, and paying only $28,000 would have left him short by $2,800 spread across four installments, with an addition to tax computed on each shortfall for the period it ran.

What the system gets right

• The prior-year safe harbor converts an unknowable obligation into a known one, which is the single most useful feature of the whole regime for anyone with variable income.
• Because withholding and estimated payments count toward the same requirement, someone with both a job and a business has two dials rather than one, and the withholding dial reaches backward in time.
• The annualized method exists precisely for income that arrives unevenly, so a genuinely back-loaded year need not produce an addition to tax.
• The under-$1,000 and no-prior-year-liability exceptions keep small and first-time cases out of the system entirely.

Where it goes wrong for people

• The installments are widely believed to be quarterly and are not: the third-quarter payment covers three months and the fourth covers four, so a calendar reminder built on quarters misses two dates.
• The addition to tax is computed installment by installment, so paying the full year's tax in April does not undo an underpayment from the previous April. It is also not deductible.
• Someone whose income rises sharply mid-year and who aims only at the 90%-of-current-year test is estimating a moving target, and getting it wrong costs money that the prior-year test would have avoided.
• A first profitable year after a year with tax liability has no cushion: the prior-year safe harbor is only free of penalty risk if the prior year actually produced tax to measure against.
• Four payment dates plus a state equivalent is real administrative work, and the money has to be set aside from cash flow that arrives on a different schedule.