Put the tax year on every deadline

April 15, 2026 does two jobs, and treating it as one date is where the trouble starts. It is the filing and payment deadline for the 2025 federal individual Form 1040 or 1040-SR return. It is also the first estimated installment for 2026 tax.

Same day, two different tax years.

So tag every date with a year before it goes on a calendar. A return filed in 2026 settles what happened in 2025. A coin sold in August 2026 creates 2026 tax, and that tax is paid in installments during 2026 with a final one on January 15, 2027.

October 15, 2026 is the filing deadline after a timely six-month Form 4868 extension, and it is not a payment date.

For the 2026 return, April 15, 2027 and October 15, 2027 are calendar-based expectations only. We checked the four 2026 installment dates against TokenTax's crypto quarterly schedule and the period pattern in the IRS estimated tax FAQ; they line up. If you came in cold, you can return to the crypto filing guide for the surrounding filing sequence.

Tax year Date What this covers What missing it can mean
2025 April 15, 2026 Filing and payment deadline for the 2025 Form 1040 or 1040-SR Unpaid 2025 tax runs the recurring late-payment charge of 0.5% per month or part-month, capped at 25%
2025 October 15, 2026 Filing deadline after a timely six-month Form 4868 extension A late return; this date never covered payment of 2025 tax
2026 April 15, 2026 First 2026 estimated installment, income from January 1 to March 31 Underpayment exposure for that period even if later installments are right
2026 June 15, 2026 Second installment, income from April 1 to May 31 A shortfall tied to that period, separate from the annual total
2026 September 15, 2026 Third installment, income from June 1 to August 31 A summer gain sits unpaid in its own period
2026 January 15, 2027 Fourth installment, still 2026 tax, income from September 1 to December 31 Late-year income left outside the installment schedule
2026 April 15, 2027 (Calendar expectation) Filing and payment for the 2026 return Balance due after installments starts accruing from this date
2026 October 15, 2027 (Calendar expectation) Extended filing date under the six-month pattern A late return; payment timing is judged separately

Work through an August 2026 gain

Every figure below is an invented teaching assumption. None of it is a research observation, a real taxpayer file, or anyone's filing history.

Assume a calendar-year individual who files single. Full-year 2025 tax was $10,000 and 2025 AGI was $120,000. In 2026 there is no withholding and no credits, and two $2,500 installments were already paid on time, on April 15 and June 15.

Then on August 20, 2026 the person realizes a $30,000 gain, and projected total 2026 tax after that gain is an assumed $18,000. That $18,000 is set by assumption, not produced by applying a rate to $30,000. To see how a rate would actually be chosen, check the applicable capital gains rate.

  1. Place the gain in its income period. August 20 falls in the June 1 to August 31 window, so the checkpoint is the September 15, 2026 installment.
  2. Run the current-year test: $18,000 × 90% = $16,200.
  3. Run the prior-year test: $10,000 × 100% = $10,000. AGI of $120,000 is under the $150,000 line, so 100% applies rather than 110%.
  4. Take the smaller annual benchmark: $10,000.
  5. Reconcile what is already in: $2,500 + $2,500 = $5,000 paid on April 15 and June 15.
  6. Continue the regular installments. $2,500 on September 15, 2026 and $2,500 on January 15, 2027 bring the year's payments to $10,000, matching the benchmark.
  7. Keep the annual balance separate. Projected tax of $18,000 less $10,000 paid leaves an assumed $8,000 due with the 2026 return, on the qualified April 15, 2027 expectation.

The smaller-of comparison answers one question: how much needs to be in by the installment dates. It does not tell this person what their tax on the gain is, and $10,000 is an annual benchmark rather than a payment instruction for anyone else.

Notice what the example assumes. April and June were paid on time. That is why the September installment works as a forward checkpoint instead of a repair job, because nothing earlier was skipped.

Concentrated late-year income outside these assumptions belongs in the timing review described further down, not in an equal-installment arithmetic like this one.

Decide whether estimated payments enter the picture

Estimated payments generally apply when you expect to owe at least $1,000 after withholding and credits, and your withholding and credits come to less than the smaller of 90% of current-year tax or 100% of prior-year tax.

Koinly's quarterly-taxes write-up carries that $1,000 trigger record, and it reads consistently with the IRS estimated tax FAQ.

The percentage side of the test is what most people skip: a person with steady wage withholding can clear both conditions without a single voluntary payment, while someone with a summer sale and no withholding clears neither.

The $1,000 is about an expected balance, not about proceeds. A broker figure showing $40,000 of proceeds is not $40,000 of income, and using the proceeds number to size a payment usually overshoots. Settle the gain against your records first, then project.

When the basis side is the shaky part, reconcile the gain before reporting it.

Before you calculate anything, collect these:

  • The return year you are working on, kept separate from the year the tax arose.
  • Prior year's total tax and prior year's AGI, plus your filing status.
  • Confirmation that the prior return covered a full 12 months.
  • A current-year tax projection, including the gain.
  • Withholding and credits expected for the current year.
  • The realization date of each gain, not just the amount.
  • Dated records of every estimated payment made so far, amount and date together.

One caution on that last line. An extension confirmation is not a payment record. They are separate documents doing separate things, and a folder holding only the first one tells you nothing about installment timing.

Compare the current-year and prior-year safe harbors

Timely withholding and estimated payments totaling at least 90% of 2026 tax, or 100% of 2025 tax, generally meet the federal individual estimated-tax payment threshold. The prior-year percentage rises to 110% when 2025 AGI exceeds $150,000, or $75,000 for married filing separately (current figure at the IRS).

The prior-year route also generally requires a full 12-month 2025 return, which is why a first filing year or a short year can quietly remove that option.

Two checks, not one. The first asks whether your annual total reaches the lower of those two benchmarks. The second asks whether the money arrived by the installment dates that applied to it.

Passing the first and failing the second is common, and the annual figure on its own says nothing about period timing. Year-specific Form 1040-ES and Form 2210 instructions are the named authorities for both the dates and the underpayment tests.

Match uneven income to payment periods

"Quarterly" is a misleading word for this schedule, because the periods are not four equal three-month blocks. Income from January 1 to March 31 is due April 15. April 1 to May 31, a two-month stretch, is due June 15.

June 1 to August 31 is due September 15. September 1 to December 31 is due January 15 of the following year, a four-month period that lands in the next calendar year.

Crypto income rarely spreads itself evenly across those windows. One sale in late November sits entirely in the fourth period, and one sale in May sits in a period that is only two months long.

For income that arrives in lumps, the researched mechanism is Form 2210 with Schedule AI, together with the Annualized Estimated Tax Worksheet in Publication 505. That approach matches the required installments to when the income actually showed up rather than assuming one quarter of the annual figure per period.

This article does not run that worksheet or produce an annualized number for you; the point here is knowing when it becomes the relevant tool.

The test is simple to apply. Look at where your income landed. If most of it hit one period, an equal-installment calculation may ask for money in periods where you had almost nothing, and the timing review is worth doing before you send the next payment.

Keep a filing extension separate from payment

Take the 2025 return as the concrete case. April 15, 2026 is the payment deadline for 2025 tax. A timely Form 4868 moves the filing deadline to October 15, 2026 and does nothing to the payment date.

IRS Instructions for Form 1040 and Form 1040-SR govern that 2025 deadline and point to Form 4868 for the automatic six-month filing extension.

Here is a hypothetical worth pinning to your own calendar habits. Someone sets an October reminder for the extended filing date, feels organized, and never sets an April reminder for the payment. The return goes in on time in October.

The tax has been unpaid since April, and the recurring late-payment rule of 0.5% of unpaid tax per month or part-month, capped at 25%, has been running the whole time. That figure comes from the 2026 revision of Form 4868, which carries draft status.

Keep that late-payment rule mentally separate from estimated-tax underpayment. They attach to different failures, and the 0.5% monthly figure is not the estimated-tax penalty calculation.

For the 2026 return, April 15, 2027 and October 15, 2027 remain expectations drawn from the recurring pattern rather than announced dates.

One scenario sits outside the ordinary calendar. A calendar-year filer who qualifies as abroad has a projected automatic two-month extension to June 15, 2027, extendable to October 15, 2027 with Form 4868. Both dates are projections, and the qualifying-abroad conditions are what determine whether they apply at all.

Being physically outside the United States on April 15 does not by itself put you in that group, and nothing in this record grants payment relief.

Check late payments and exceptions before your next step

A correct amount can still be a late amount.

Paying on April 20 instead of April 15 can create a penalty for that period even though the figure was right, which is the professional commentary point in SDO CPA's quarterly guide and reads consistently with the IRS underpayment page.

The second hypothetical mistake to watch for is exactly this one: assuming a payment that is only a few days off, but accurate, is automatically penalty-free.

Paying everything at annual filing does not reach backward and fix a period that was short. The annual balance and the installment history are judged separately, which is the same split that runs through this whole calendar.

Postponed deadlines do exist, and they are localized. Relief applies to taxpayers in specific declared-disaster areas under published eligibility rules, so it is not a general extension you can assume into your own plan. State payment rules are not covered here either.

Your next step is a records step. Open your payment history, write the date next to each amount, and assign each one to the period it was meant to cover.

Then revisit reconcile the gain before reporting it and check the applicable capital gains rate to firm up the projection those payments are aiming at.

Gather your payment records and dates, then check the applicable capital gains rate before updating your estimate.

Sources

Publication 509 (2026), Publication 505, and Form 2210 Schedule AI appear as named documents in the underlying research; their roles here are limited to what those records describe. The 2026 estimated-payment dates and the safe-harbor percentages above rest on general 2026 knowledge accepted for this page, with the IRS as the publisher of the governing figures.