2026 Important Financial and Tax Dates

Estimated tax payments run on a quarterly schedule that doesn't match the calendar quarters most people assume. For 2026, the four due dates are January 15 (covering the prior year's Q4), April 15 (Q1), June 15 (Q2), and September 15 (Q3). If you have income that isn't subject to withholding, a business, RSU vesting, a large capital gain, or a Roth conversion, missing one of these payments generates an underpayment penalty even if you pay everything owed by the following April.

April 15 is the single busiest date on the calendar and it carries more than just the 1040. It's also the gift tax return (Form 709) deadline if you made gifts requiring one, the deadline to request the automatic six-month extension (Form 4868) for both, the Q1 estimated payment date, and the deadline to make a prior-year contribution to an IRA or HSA. That last one is the one people miss most often: the contribution window for last year's IRA or HSA doesn't close December 31, it stays open until you file, right up to April 15, which means there's still time in the new year to fund a prior-year contribution if you haven't maxed it out.

Medicare has two enrollment windows that get confused with each other constantly. The General Enrollment Period, January 1 through March 31, is for Parts A and B and for Medicare Advantage open enrollment. The Annual Enrollment Period, October 15 through December 7, is for people already enrolled who want to switch plans, drop or add Part D coverage, or move between Advantage and original Medicare, effective the following January 1. If you're still covered by an employer plan past 65, neither window is your on-ramp, that's a separate special enrollment period tied to when your employer coverage actually ends.

Required Minimum Distributions have two distinct deadlines that only overlap once. The ongoing annual deadline is December 31, satisfy the year's RMD by then or face the penalty. But your very first RMD gets a one-time grace period: the Required Beginning Date is April 1 of the year after you turn 73, not December 31 of the year you turn 73. Taking advantage of that grace period means two RMDs land in the same calendar year, which can push you into a higher bracket, so it's worth modeling before you decide to wait. Multiple traditional IRAs can be aggregated into a single RMD, inherited IRAs cannot be aggregated with your own IRAs, and RMDs from employer plans generally have to be calculated and taken separately, other than 403(b)s, which can be aggregated among themselves.

If you're the beneficiary of an account with multiple beneficiaries, two dates matter that almost nobody tracks. September 30 of the year after death is the determination date for identifying the designated beneficiaries who set the distribution rules for everyone. December 31 of that same year is the deadline to divide the account into separate inherited accounts if you want separate accounting, meaning each beneficiary's own life expectancy or 10-year rule applies to their share rather than everyone being bound by the oldest or least-favorable beneficiary's status.

Business filing deadlines split cleanly by entity type, and mixing them up is a common source of late-filing penalties. S-corporations and multi-member partnerships (Form 1120S and Form 1065) file by March 15, with K-1s due to owners the same day. Sole proprietorships, single-member LLCs, and calendar-year C-corporations (Form 1120) file by April 15, alongside the individual 1040 deadline. Both tracks get an automatic six-month extension if you file the right form (7004 or 4868) by the original deadline, but an extension to file is never an extension to pay what's owed.

A handful of other dates round out the calendar and are easy to lose track of because they don't repeat monthly. FAFSA for the upcoming academic year opens December 1, with the deadline for the prior academic year falling June 30. Health Insurance Marketplace open enrollment runs November 1 through mid-January for coverage starting January 1, but December 15 is the real deadline if you want coverage to begin exactly on January 1 without a gap. And any marital status change, gift, Roth conversion, or charitable contribution has to be completed by December 31 to count for the current tax year, there's no extension mechanism for those the way there is for filing paperwork.

The dates that require an actual decision, Roth conversions, charitable gifts, tax-loss harvesting, HSA and 401(k) contribution elections, all have a hard stop at December 31. The dates that are just paperwork, filing the return itself, contributing to an IRA for the prior year, requesting an extension, have more room to breathe into the following spring. Knowing which category a given deadline falls into changes how much urgency it deserves in November versus April.

If you're within a few years of your first RMD, or already managing them, put September 30 and December 31 of a beneficiary year on your calendar now, not after an account holder passes away. Those two dates permanently lock in how flexible the distribution rules are for whoever inherits, and they can't be revisited once they pass.

• Assuming the IRA and HSA contribution deadline is December 31 when it's actually the tax filing deadline the following April, missing a full extra three and a half months of contribution room.
• Confusing Medicare's General Enrollment Period (January to March, for new enrollment) with the Annual Enrollment Period (October to December, for existing enrollees switching plans).
• Waiting until April to make a Roth conversion, harvest a loss, or complete a charitable gift for the prior year, none of which can be done after December 31 regardless of extensions.
• Not tracking the September 30 and December 31 beneficiary deadlines after an account owner's death, which permanently forecloses the option for separate accounting among multiple heirs.
• Treating a filing extension as a payment extension. An extension moves the paperwork deadline, not the date the tax owed is due.