An 83(b) election is a short notice you send to the IRS saying, in effect: tax me on my restricted founder stock now, at today's value, instead of taxing me later, piece by piece, as it vests. Because "today's value" at incorporation is usually close to nothing, the tax due now is usually close to nothing too.
You have 30 days from the date the stock is issued to you. Not from when you learn about the rule. Not from your first funding round. Thirty days from issuance, and the window does not reopen. Ever.
This is a United States tax mechanism, and it is one of the very few topics in startup law where a missed deadline cannot be fixed by any amount of money or lawyering afterward.
The scene where it goes wrong
A founder incorporates a Delaware C-corp and signs a stock purchase agreement. Her shares are subject to vesting: four years, one-year cliff, the standard package. Her lawyer sends a one-page 83(b) form with a note saying "file this within 30 days." She is heads-down on the product. The page sits in a drawer.
Two years later the company raises at a real valuation. Now, at every monthly vesting date, the IRS treats the value of the newly vested shares as ordinary income, income she must pay tax on, in cash, for shares she cannot sell. The paper she left in the drawer would have cost her nearly nothing. Skipping it can cost more than her salary.
The 83(b) is the cheapest insurance in startup law: one page, thirty days, filed once.
Why founder stock triggers this at all
The 83(b) question exists because founder shares are usually restricted: issued to you immediately, but subject to vesting, meaning the company can repurchase the unvested portion if you leave. Under the default US tax rule, restricted stock is taxed as it vests, at its value on each vesting date.
That default is a trap for founders of anything that succeeds: your tax bill grows exactly as fast as your company does. The 83(b) election flips the timing: you are taxed once, up front, on the (near-zero) value at issuance, and the future growth is later treated under capital gains rules when you actually sell.
If your shares are worthless today and might be valuable tomorrow, you generally want that flip. Which describes essentially every founder at incorporation.
Before incorporation: nothing to file yet, but plenty to anticipate
The Founder Notes distinction applies here with unusual force. Before incorporation there are no shares, so there is nothing to elect: the 83(b) clock starts at issuance, not at the founder agreement. A team building on a pre-incorporation agreement has no 30-day problem yet.
But the founder agreement is exactly where you anticipate it. A good one records that founder equity will be subject to vesting at incorporation, that the vesting start date may be backdated to credit work already done, and that each founder will handle their tax filings, the 83(b) chief among them, within the deadline at issuance. When investors later impose vesting on already-issued shares, the question can resurface, which is one more reason to get the sequencing right the first time.
The founder agreement cannot file the 83(b) for you. It can make sure nobody discovers the rule in month thirteen.
How founders actually file
Mechanically, the election is a short statement filed with the IRS within 30 days of issuance. The IRS now provides a standardized form for it (Form 15620), and an electronic filing option has been introduced alongside the traditional mailed letter. Founders typically keep proof of timely filing forever, because the one question every future acquirer's counsel asks is: "did every founder file their 83(b) on time?"
Two practical rules. First, calendar the deadline the day you sign your stock purchase agreement. Second, do this with a tax advisor: the election is simple, but your situation may not be, especially for non-US founders holding US stock.