Overview

If you work for a tech startup, it’s likely you’ve been granted incentive stock options (ISOs). 

Hopefully they’ll make you money someday. But how much you’ll make depends for a good part on how they’re taxed.

It isn’t easy to educate yourself on this. 

Most info isn’t specific to the tech startup situation. Or it’s written in jargonese. Or it’s too high-level to be practically useful.

That’s why we put together this guide: 

An in-depth resource on ISO taxes and strategies — written in plain English — with helpful visualizations.

Still have questions? Feel free to hit us up for a chat in the bottom-right. ↘️ 

Note: this guide is complete, but a little simplified

ISO taxation is a rabbit hole of complexity – mainly because of the alternative minimum tax (AMT).

The page you're on now fully explains ISO taxation, but we've simplified the part about AMT.

That means you'll get the key takeaways, but you won't grasp why it works like this – and there will be some edge cases that this explanation won't cover.

For most startup employees, that will be more than enough.

But if you're the type of person who doesn't want to cut any corners, we'll show you how deep the rabbit hole goes. Feel free to read this page first, and then take the AMT Deep Dive as a supplement. Enjoy 🐰

TL;DR

If your company exits and you sell your ISOs, the money you make is taxed. 

But you get a major tax discount if you exercise them at least 12 months before selling (and you don’t sell them within 24 months after grant).

The problem? You already need to prepay a part of the taxes the moment you exercise.

If you can’t afford that, then you can't exercise and you miss out on the overall tax discount.

What makes it extra tricky is that the later you exercise, the more tax you'll need to prepay – assuming your company is growing (and its 409A valuation keeps rising).

So...

To get the most out of your ISOs when your company IPOs, exercise them at least 12 months before you sell them. And the earlier you exercise, the less cash you need to do so (assuming your company is growing).

Warning: when you exercise, your employer won't withhold the taxes you owe. It’s up to you to pay them.

(Want to know exactly how much you'll be taxed? Use our free Exercise Tax Calculator for taxes on exercise and the Profit Simulator for taxes on sale.)

What are ISOs?

Incentive stock options (or ISOs) are a type of stock option that get a more favorable tax treatment than other types of stock options. When early stage tech startups give you equity compensation, it’s usually ISOs.  

ISOs vs NSOs: what’s the difference?

With ISOs, you’re less likely to be taxed when you exercise them than with NSOs. And if you are taxed, it’s at a lower rate.

Then later, when you make money with them, you’re taxed again at an effective rate that’s often lower than with NSOs (more on that later).

ISOs can only be given to employees, and are specifically meant as a form of employee compensation. Startups can award NSOs more broadly, for instance to external advisors. 

Finally, exercising ISOs is taxed under the alternative minimum tax system rather than the regular tax system. This makes it much more complicated to fully understand, but it does create the opportunity for some advanced tax optimizations.

The big picture: what’s the best tax strategy for your ISOs?

Before the rest of this guide dives into the details, let’s take a holistic look.

If you work for a constantly growing startup that ends up succeeding, the best tax strategy is to exercise your ISOs as early as possible.

That’s because:

Here’s a real-world example:

Say you join a startup and get 15,000 NSOs with a $3 strike price. Eventually, the company IPOs and you get to sell the shares for $150 each.

Over time, the 409A valuation of your company grows. (The 409A valuation is also known as the fair market value – more about it here.)

Say this is the timeline:

Then this gives 5 distinct moments at which you could exercise:

When should you exercise your ISOs?

You could exercise at any of these points in time – but the tax implications would be different at each.

Depending on when you exercise, the amount of cash you need to exercise as well as your net profit change.

Here’s the amount of cash you’d need to exercise at A, B, C, D or E:

If you wait all the way until you sell (point E), you don’t need any cash to exercise — because you can cover the costs with your proceeds.

But if you exercise before selling, you need to pay out of pocket. 

And the higher the 409A, the more cash you need. (Because you trigger a higher tax bill – but more on that below). 

So why exercise before selling? 

Because if you don’t, you end up with the lowest possible net profit:

If you exercise at least 12 months prior to selling – which is the case at A, B and C – your net profit is higher. 

In summary, here's what happens depending on when you exercise:

Why it works like this 🤔

Normally, the money you make from ISOs is taxed just like your salary. 

But if you exercise your ISOs at least 12 months before selling them – and sell them at least 24 months after grant – you get a tax discount. 

That can increase your net profit by up to 27% – that’s what we saw in the green bar chart.

The problem? 

  1. As soon as you exercise, you have to prepay a part of these taxes
  2. And the higher the 409A valuation of the company, the more tax you need to prepay
  3. For growing startups, this effectively means: the later you exercise, the more tax you need to prepay – because if a startup is growing, its 409A increases over time

That’s what we saw in the red bar chart – rising costs over time.

Essentially, exercising before an IPO is a trade-off: it means paying some tax now so you’ll pay less tax overall.

In our example, this is what the taxes do depending on when you exercise:

Might want to stare at that for a minute to grasp what’s going on – this is confusing stuff 😵

So:

If you work for a constantly growing startup, you can maximize your net profit by exercising in advance of the exit. 

And the earlier you do this, the less cash you need.

What if exercising my ISOs is too expensive?

Of course, $206k or even $416k is a huge amount to pay for your ISOs.

Unfortunately, these are pretty common numbers for employees at the most successful and high-growth startups. 

See, for example, how much these Snowflake and DoorDash employees had to pay. Among Secfi users, the average exercise cost is $505,923

Even if you have that kind of money, putting your personal savings on the line is risky since it’s not guaranteed that your company will actually manage to reach a successful exit.

So what do you do if you still want that tax savings? Or what if you recently left your company and now have a deadline to exercise your NSOs? 

That’s exactly why exercise financing exists, which is what we offer at Secfi. 

Here’s how exercise financing works:

We make money only if there is a successful exit. If there is, you’ll pay us back more than the original amount. (But because of the tax savings, you’re often still at a net benefit vs not having exercised.)

If there’s no exit, you don’t owe us anything (and we’ll take the hit). 

See www.secfi.com/products/options-exercise to check if exercise financing is available for you, and at what rates.

Is it always better to exercise my ISOs as early as possible?

No. 

In the example above, we made two assumptions:

  1. Your company successfully exits (i.e. you get to sell your ISOs at a profit)
  2. The 409A valuation of your company keeps rising

Regarding #1, most startups never get to that point. 

That’s why exercising early is risky. If the company goes out of business, you’ve lost the money you spent. (You may be able to recover some of the taxes – but more on that in a future blog post.)

If you want to exercise your ISOs but don’t want to risk losing money, non-recourse financing is a solution.

Regarding #2, sometimes the 409A valuation of a company temporarily dips. This means you can exercise at a lower cost, so in that scenario waiting actually makes it cheaper. 

This is uncommon, but it happened at Airbnb

They could justify a lower 409A valuation when the business was impacted by covid, which enabled employees to exercise at a tax discount (before the 409A went up again shortly after).

It’s difficult to time this, however. 

If you are long-term optimistic about the company, you should expect the 409A valuation to go up – unless you foresee a specific reason why the company would take a hit in the short term.

Now that you’ve got the big picture, let’s dig into the details of just how ISOs are taxed…

So how exactly are ISOs taxed?

ISOs are taxed twice:

  1. When you exercise them
  2. Then again when you make money with them after your company exits

At exercise, ISOs are taxed at alternative minimum tax (AMT) rates. The higher the 409A valuation of your company, the more you owe.

When you make money selling them, they’re taxed at ordinary income rates (the highest possible rate, just like your salary).  

Unless...

If you exercised them at least 12 months prior to selling (and sell them at least 24 months after grant), you pay long term capital gains rates instead. That’s a lower tax rate, increasing your net profit by up to 27%. More details on how this works below.

Whatever you paid at #1 will be subtracted from your liability at #2 – your exercise tax acts like a prepayment for your future sale tax. (You’re not double taxed!)

Are ISOs taxed when initially granted?

No. There’s no tax due when your company initially grants you the ISOs (i.e. awards you with them).

Are ISOs taxed when they vest?

No. After grant, most ISOs follow a vesting schedule that dictates when you actually ‘get’ them. But when they vest, there’s still no tax due.

How are ISOs taxed when exercised?

In short:

Let’s go through it step by step:

When you exercise an ISO, you pay its strike price to your company to buy a share. Say you have ISOs with a $3 strike price:


But even though you’re not making money, the difference between the strike price and the current 409A valuation is considered a phantom profit (also known as the spread) by the IRS.

Say the current 409A valuation is $35 per share. If you pay $3, you’re making a $32 phantom profit in the eyes of the IRS.


This phantom profit gets taxed. And that tax is called the alternative minimum tax (AMT).

Impressive how complicated they managed to make this, no? A true work of fiscal art...

If you’ve made it this far, it’s time to dive into:

ISOs and the Alternative Minimum Tax (AMT)

You might not have heard about the AMT. It's a tax you normally don't encounter, but it kicks in when exercising ISOs. 

It’s a weird tax with its own set of rules. 

In this guide we’ll just share the takeaways. (You can read our AMT Deep Dive for details.)

For our clients in California, the AMT is usually ~30-38%. We’ll assume 35% in this article.

In our example, a 35% rate means that each ISO you exercise builds up $11.20 of AMT:


However, you don’t necessarily owe $11.20 dollar of AMT per ISO you exercise.

That’s because each year you have a tax-free AMT threshold. 

Say your AMT threshold is $7000, then you only pay the dollars of AMT that go beyond that $7000. If you stay under that $7000, the AMT won't kick in and you owe nothing at all.

So whether you reach the threshold and actually owe AMT depends on the number of ISOs you exercise: 

The $7000 here is just an example. Your AMT threshold is probably a very different dollar amount. It totally depends on your tax situation for the year. 

In fact, the AMT threshold isn't really a thing – as in, it's not defined and set by the government. Rather it's a result of the inner workings of the AMT, which effectively give you a threshold. If you're interested, the AMT Deep Dive goes in-depth.

For the purposes of this guide though, all you need to know is that:

Here’s a real-life example:

Say in total you have 15,000 ISOs. (The rest of the numbers are the same as before: $3 strike price, current 409A valuation is $35, and your AMT threshold for the year is $7000.)

If you exercise all 15,000, then:

But you only have to pay the AMT that surpasses your $7000 threshold, so in the end your tax liability is $161,000 ($168,000 − $7000).

Adding the taxes to the $45,000 strike price, and your total exercise costs are $206,000.


Note: The tax you pay when exercising isn't additional. It’s frontloaded. That means it gets subtracted from the tax you owe when you sell your shares at a profit, and won’t affect the overall net amount you make. 

Wait – aren’t ISOs supposed to be tax-free to exercise?

No. They’re often touted as such, but that’s a dangerous misconception. 

The idea is that they are in principle tax-free, and the AMT is just an ‘exception’ that kicks in if you exercise a lot of ISOs (driving the AMT beyond your yearly threshold). 

The problem is that many employees reach that threshold pretty quickly.

Warning #1: your employer won’t withhold this tax – you pay it when you file your taxes

Sometimes employers don’t even notify their employees of their ISO tax liability. And it’s your responsibility to pay this to the IRS. 

In some cases, even tax advisors aren’t aware of this. We’ve heard horror stories of accountants letting their clients know that they owed an extra $60K — the day before taxes were due. 

Warning #2: the later you exercise, the higher your tax liability can become

If your company keeps growing, then exercising your ISOs becomes increasingly expensive over time. 

And the faster the company grows, the worse it gets.

This is because of the 409A valuation. The higher the 409A, the larger your phantom profit, the more tax you’ll owe. 

The 409A is updated at least yearly and reflects company growth. If the company is in a better place than last year, the 409A will rise.

(The 409A valuation is an appraisal of the value of a company share for tax purposes. By law, your employer is required to have it re-assessed by a third party at least once a year – or when something substantial happens to the company, like a new funding round.)

Example:

Say the 409A valuation of your company grows from $35 now to $50 one year later and $75 two years later:


Then the total cost to exercise your 15,000 ISOs (including AMT) grows from $206,000 to $284,750 to $416,000:


Exploding exercise costs effectively lock you out from exercising your ISOs. 

This is especially a problem at high-growth startups. As mentioned earlier, Snowflake and DoorDash are good examples.

Tip: if your employer allows early exercising, you can exercise tax-free

A higher 409A valuation means more taxes, but this also works the other way around. A lower 409A means less taxes. 

And if the 409A is equal to your strike price, you pay no taxes at all (because your phantom profit is zero).

That’s the case when you’re first granted your ISOs, because your strike price will be set to the 409A valuation at the time. So if you exercise before the 409A valuation goes up, it’s tax-free.


You can only do this if your company allows early exercising: exercising options before they vest. 

At most companies you’ll have to wait for your ISOs to vest instead. But by that time, it’s likely the 409A has already increased.

⚠️ Warning: if you early exercise, you need to file an 83(b) election with the IRS within 30 days. This makes it official. If you forget to file it, you’ll still be taxed when your ISOs vest in the future.

Use an ISO tax calculator to figure out your exact tax burden

In the above examples, we’ve used an effective AMT rate of 35%, which is what we often see among our clients in California. But it really depends on:

If you want a personalized figure, use our Exercise Tax Calculator. It’s completely free. Just create an account, enter your tax and equity details and it runs the numbers for you.

How are ISOs taxed when you make money (i.e. sell them after an exit)?

When you make money by selling your equity in an IPO or acquisition, your profit – ie. the sell price minus strike price – is taxed.

With ISOs, your profit either gets taxed either as:

By default, you get the ordinary income tax rates – that's the highest possible tax rate, and the same as your salary.

But

If you exercised your ISOs at least 12 months before selling them, you get the lower long-term capital gains rates. 

Lower rates means your net profit is higher: the gain can be up to 27%.

If you exercised before and already paid taxes over your phantom profit, then that gets subtracted from your sale taxes. (You’re not paying double tax 🙌.)

Real-life example with ordinary income rates:

Again, let’s say you have 15,000 ISOs at a $3 strike price. And you exercised them when the 409A was $35. 

After the IPO, you can sell them for $150 each. 

In this example, however, you exercised less than a year from the IPO, so you don’t get the tax discount.

The money you make is taxed at ordinary income rates. 


In this example we’ll use 45% for federal + California taxes, but the actual rates depend on your situation. Use our free Profit Simulator for a personalized figure.

Assuming 45%, your situation now looks like this:

Your net profit is $80.85 per ISO.

But when you exercised your ISOs earlier, you already paid $45,000 for the strike price and $161,000 in taxes.

So if you now sell all of your 15,000 ISOs, this happens:

Your net profit is $1,212,750.


ISOs and long-term capital gains tax

Now let's look at what happens if you do get the tax savings.

Same scenario, except this time you exercised more than 12 months before selling, so you’re taxed at long-term capital gains rates. 


Again, the actual rates depend on your situation – in this article we’ll use 30% for federal + California.

The calculation is pretty much the same:

Your net profit is $102.90 per ISO.

Selling all of your 15,000 ISOs gives:

Your net profit is $1,543,500.


The benefit of long-term capital gains rates for ISOs

Exercising your options before the IPO is costly and risky, but the tax savings can be worth it.

In our example:

The difference is $330,750, a 27.3% gain.


For early employees at highly successful startups, the gain can be tens to hundreds of thousands of dollars. We mentioned them couple times already, but these Snowflake and DoorDash case studies are again good real-life examples.

How are ISOs taxed when you exercise and sell at the same time (i.e. a cashless exercise)?

Stock options are often explained as:

  1. You first pay money to exercise them, buying you a share
  2. Then, later, you sell that share at a profit (hopefully)

But #1 and #2 can happen at the same time – you buy the share, then immediately sell it. It’s as if you directly sold the ISO (rather than a share).

Of course, you can only do this if you wait until your company exits (otherwise its shares aren’t sellable). 

This is called a cashless exercise, since you don’t have to come up with the cash to cover the exercise costs. 

You immediately make money – the immediate costs are withheld from your proceeds, and you’re guaranteed to have enough cash to cover any taxes later on.

Waiting for an exit to do a cashless exercise is a popular strategy because exercising prior to the exit can be expensive and risky (after all, there’s no guarantee of a successful future exit).

Tax-wise, this means that you don’t get the long term capital gains tax discount. 

The two taxable events – exercising and selling – blend into one. So since you didn’t exercise at least a year prior to selling, your profit gets taxed as ordinary income rather than long-term capital gains.

Hope that was helpful
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