The real cost of exercising your startup stock options — and 3 ways to cover it

The strike price is only half the bill. Exercising ISOs or NSOs can trigger a tax charge in the same year — before you've sold a single share. Here's the full cost, and three practical ways people actually cover it.

When employees think about exercising their stock options, they usually look at one number: the strike price × the shares. That's the cost to buy the shares. But for US option-holders it's often not the whole bill — because exercising can create a tax charge in the year you exercise, even if you never sell. Miss that, and an affordable-looking exercise turns into an unexpected five-figure surprise.

Where the tax comes from (ISOs vs NSOs, briefly)

Which tax you face depends on the type of option you hold:

• ISOs (Incentive Stock Options). Exercising doesn't create ordinary income, but the bargain element — the difference between the current value and your strike price — can feed into the Alternative Minimum Tax (AMT) for the year you exercise. Depending on your overall tax picture, that can produce a real AMT bill even though you've sold nothing.
• NSOs (Non-qualified Stock Options). The bargain element is generally taxed as ordinary income at exercise — so the tax event happens then, not when you eventually sell.

This is a practical summary, not tax advice — the exact result depends on your income, deductions and situation, so confirm with a tax professional. The point for planning is simple: don't budget only the strike price.

Why the tax can land before you see any cash

Private-company shares are illiquid. You can exercise, hold the shares, and owe tax on a paper gain — with no market to sell into to raise the money. That mismatch (a tax bill now, cash maybe years away) is the single most common thing that catches option-holders off guard, especially after leaving a company.

Three ways people cover the cost

Once you know the real number, there are broadly three ways to fund it:

• 1. Pay out of pocket. Simplest if you have the cash and conviction. But committing a large sum to an illiquid, uncertain asset is a genuine risk — size it against your finances, not your hopes.
• 2. Time it. Exercising earlier, when the bargain element is smaller, can mean a smaller AMT adjustment — but you're betting on a company that might not make it. Exercising in a year with room under the AMT thresholds is another lever. This is where a conversation with a tax adviser pays for itself.
• 3. Sell a slice to fund the rest. Many people exercise and then sell part of the shares to a private buyer — using the proceeds to cover the exercise cost and the tax, while keeping some upside. This is exactly the situation a secondary sale is built for, and it's what we help arrange.

The 90-day trap for leavers

If you've left (or are leaving) a US company, watch the post-termination exercise window — often around 90 days, though it varies and some companies extend it. Vested options you don't exercise in time can simply expire. That deadline is what forces the "exercise now, find the cash somehow" scramble, and it's the moment the three funding routes above become urgent rather than theoretical.

Before you exercise, check

• Whether your options are ISOs or NSOs
• Your strike price and the current 409A / latest value — the gap is the bargain element
• The total cash needed: strike cost plus the estimated tax (the calculator does this)
• Any exercise deadline if you've left
• Whether the resulting shares are transferable — if you might sell a slice to fund it, check the right of first refusal and transfer rules first
• Your specific position with a tax professional before committing real money

Read next

• Can an ex-employee sell startup shares?
• Who buys private startup shares — and how to actually sell yours
• How much are my startup shares worth?

Further reading

General, independent references on how private-company shares and options work. We're not affiliated with any of them.

• Carta — cap tables, secondaries and valuation explainers
• Cooley GO — startup legal explainers, including rights of first refusal
• Forge Global and EquityZen — secondary marketplaces (larger, later-stage deals)
• Ledgy and Index Ventures OptionPlan — European equity & ESOP references

General information only — not financial, tax or legal advice. Every situation is different; check your own share and option agreements and take professional advice before selling. PrivateTechShares makes introductions only: it is not a broker, does not hold funds, and does not execute or advise on transactions.