Tax Due Dates

The next twelve months

The end-of-year row is the one worth circling. Most of what actually lowers a tax bill has to happen inside the tax year. By the time a return is being prepared in March, nearly every lever has already moved. The exceptions are narrow: an IRA or HSA contribution can still be made up to the April deadline, and a SEP-IRA can be funded as late as the extended due date of the return.

The 2026 tax year, end to end

The same calendar arranged by who it applies to, including the dates that have already gone by, so you can see the whole shape of a filing year in one place.

Two things people get wrong every year

An extension moves your filing deadline, not your payment deadline. If you owe, that money is still due on the original date. Filing an extension without paying an estimate of what you owe means interest and a late-payment penalty accrue from April regardless. The extension does spare you the much larger failure-to-file penalty, so it is still worth filing one — just pay something with it.

The S-corporation election deadline is not the return deadline. Form 2553 has to be filed within two months and fifteen days of the start of the tax year you want it to apply to — March 15 for a calendar-year entity — or at any point in the preceding year. Deciding in November that you wish you had been an S-corp all year is the most common version of this, and there is a late-election relief procedure, but it is a procedure with conditions, not a formality.