The short version
Equity comp runs on a handful of clocks. A few are firm, rarely-changing rules, like the roughly 30-day window to file an 83(b) election and the holding periods that decide how your ISO sale is taxed.
Others are specific calendar dates that shift year to year, like the annual filing deadline and quarterly estimated-tax due dates. This page describes the rules in general terms and flags the dates you should confirm for your year before relying on them.
This is a general reference, not a personalized calendar, and not tax advice. The fixed rules below are stable, but specific filing dates (like quarterly estimated-tax due dates and the annual return deadline) can shift year to year. Confirm any exact date for your year before acting on it. Last updated: June 2026.
83(b) election window
If you want to make an 83(b) election on restricted stock or early-exercised options, you generally have about 30 days from when the stock is transferred to you to file it (you can now use IRS Form 15620, including online). There is generally no extension and no relief for missing it, which makes this the least forgiving clock in equity comp.
ISO qualifying holding period
To get the most favorable tax treatment on incentive stock options, the general rule is to hold the shares more than two years from the grant date and more than one year from the exercise date. Meet both and a sale is usually a qualifying disposition; miss either and it is disqualifying.
AMT from an ISO exercise
If you exercise and hold ISOs, the AMT effect lands on the tax return for the year you exercised, and any tax is due with that year's filing. The federal individual filing deadline is generally April 15 (it was April 15, 2026, for 2025 returns). It can shift when the 15th falls on a weekend or holiday, so confirm the date for the year that applies to you. An extension to file is not an extension to pay.
RSU income at vesting
Restricted stock units are generally taxed in the year they vest, on the value at vesting. That income belongs on that year's return, and a large vest can change your withholding and estimated-tax picture for the year.
Estimated tax payments after a windfall
A big exercise, vest, or sale can create income that was not fully withheld, which may require quarterly estimated tax payments to avoid an underpayment penalty. The federal due dates fall roughly quarterly: for the 2026 tax year they are April 15, 2026, June 15, 2026, September 15, 2026, and January 15, 2027. Dates shift slightly year to year and for weekends and holidays, and your state may have its own schedule, so confirm the dates that apply to you.
Company information forms
After certain equity events, your company furnishes information forms: Form 3921 for ISO exercises and Form 3922 for the first transfer of ESPP shares. These are generally furnished to you by January 31 for the prior year's activity. NSO and RSU income, by contrast, shows up on your W-2. Having these in hand makes filing (and getting your cost basis right) much easier.
Where this trips people up
Treating the 83(b) window as flexible
It is not. The roughly 30-day clock starts when you receive the stock and generally allows no extension. If an election makes sense, it has to go out right away.
Forgetting estimated taxes after a windfall
A large exercise or sale can create tax that withholding did not fully cover. Waiting until April can mean a balance due plus an underpayment penalty.
Assuming withholding covered an exercise
Withholding on equity income is often below your real rate. Check the gap when you exercise or vest, not when you file.
Miscounting holding-period clocks
The ISO clocks start at different events (grant versus exercise), and both have to be met. It is easy to miss one and turn a qualifying sale into a disqualifying one.
Deadline questions people ask
When are estimated taxes due?
They fall roughly four times a year: mid-April, mid-June, mid-September, and mid-January of the following year. The exact dates shift slightly year to year, so confirm the current year's schedule (the dates above are for this year).
Why would I owe estimated taxes on my equity?
Because withholding on RSUs and NSOs is often less than your real tax rate. When that happens, you may need to make quarterly estimated payments to cover the gap and avoid an underpayment penalty.
What is the deadline for an 83(b) election?
30 days from when the stock is transferred to you. It is firm and cannot be extended, so it belongs on your calendar the moment you receive the stock.
What are Forms 3921 and 3922?
Informational forms your company provides. Form 3921 reports an ISO exercise; Form 3922 reports an ESPP transfer. You generally receive them by the end of January, and they carry numbers you will need at tax time.
When is my tax return due?
Generally mid-April, with an extension available to October. Keep in mind that an extension to file is not an extension to pay; taxes owed are still due in April.
How do I avoid an underpayment penalty?
Generally by paying in enough during the year, through withholding and estimated payments, to meet a safe harbor based on your prior-year or current-year tax. A spike from an equity event is a common reason people fall short, so it is worth checking mid-year.
Keep reading
ISOs and AMT
Why an ISO exercise can create a tax bill before you sell, explained. →
The 83(b) election
The deadline that gives this page its most unforgiving clock. →
RSUs and how they're taxed
Vesting drives the timing for RSUs. Here is the full picture. →
All resources
Browse every equity-comp explainer in one place. →
Have a deadline coming and want to get it right?
Keeping these clocks straight, and planning the cash and the filings around them, is a lot of what I do with clients. If you have an equity event on the horizon, I am happy to help you stay ahead of the dates that matter. Here is how to start a conversation.
Become a ClientThis article is general information, not tax or legal advice for your specific situation. Tax outcomes depend on your individual facts, and the rules change over time. Talk to a qualified professional (I am happy to be that person) before acting on anything here. Reading this page does not create a client relationship.