net investment income tax and the 3.8% surtax

In short

A friend of mine sold a rental house one spring and was surprised by a tax line he had never heard of. It was the net investment income tax, an extra charge the law puts on certain investment earnings. If you have a high income, you may owe it on top of regular tax. It applies only when your modified adjusted gross income, or MAGI, passes a limit set by law for your filing status. The tax falls on the smaller of two amounts: your net investment income, or the part of your MAGI above that limit. The IRS reports it on Form 8960, and it appears in the instructions for that form on irs.gov. Wages are not part of the tax base, though they can push you over the limit. So check your MAGI before you sell anything big.

The whole of it

What it is

I once sat beside a retired schoolteacher who had never paid more than a modest tax bill in her life. Then she sold a small piece of land her father left her, and the number on her return gave her a start. She was not in trouble. She had simply met a tax most people never meet.

The net investment income tax, often called NIIT, is a 3.8 percent surtax. A surtax is an extra tax added on top of the tax you already pay. It was created by the Affordable Care Act and is found in section 1411 of the Internal Revenue Code. The IRS explains it on its page about the net investment income tax. It is a separate tax from your income tax. It does not change your tax brackets. It simply sits beside them.

It reaches people whose income is above a limit. That limit is not adjusted each year for inflation. The statute fixes it, which is a quiet reason more families run into it as the years pass. Many people are glad to learn that. It means the rule does not creep up on a schedule. It stays where the law put it, at the current figure, which the official source publishes each year for a single filer.

How it works

If you are holding stocks, bonds, or a rental property, you have probably wondered what counts. Net investment income includes interest, dividends, capital gains, rental income, royalties, and certain annuity income. It also includes income from a business where you take no active part. The word net means you may subtract the costs tied to that income, such as investment interest expense and certain state taxes.

Some things are left out. Wages and self employment income are not net investment income. Neither is a payout from a qualified retirement plan, like a 401(k) or a traditional IRA. Interest from tax exempt bonds is also left out. Gain from selling your main home may be shielded too, up to the limit set in the law.

Now the part people miss. The tax is not on all your investment income. It is on the smaller of two amounts. The first is your net investment income. The second is how far your MAGI sits above the limit for your filing status. Pick the lower one, then take 3.8 percent of it. That is the whole machine.

MAGI starts with your adjusted gross income. For this tax, you add back certain foreign income that was excluded. For most families the two numbers are close, or the same.

The numbers, and where to find yours

I have always found it easier to trust a number I looked up myself. Here are the ones to find. The rate is written into section 1411 of the Internal Revenue Code, and the Form 8960 instructions on irs.gov show it. The limit depends on your filing status, and the law sets a different one for single filers, joint filers, and married people filing apart. They are the current figure, which the official source publishes each year for single filers, the current figure, which the official source publishes each year for married couples filing jointly, and the current figure, which the official source publishes each year for married people filing separately.

To find your own MAGI, look at line 11 of your Form 1040, which shows adjusted gross income. Then read the Form 8960 instructions to see if anything must be added. To find your net investment income, add up the interest, dividends, gains, and rental income on your return. Then subtract the allowed costs. The IRS publishes Form 8960 and its instructions on irs.gov, and those are the sources to trust.

A worked example

Let me tell you about a man named Walt. Walt is single and works as a welder. He earns $140,000 in wages. He also sold some shares at a gain of $40,000 and earned $5,000 in dividends. So his net investment income is $40,000 plus $5,000, which is $45,000.

His MAGI is $140,000 plus $45,000, which is $185,000. Suppose the limit for a single filer is $200,000. His MAGI is below that. So Walt owes nothing under this tax. Good news for him.

Now picture a second year. Walt gets a raise to $170,000 in wages. He sells a rental property and reports a gain of $60,000, with $5,000 in dividends. His net investment income is $65,000. His MAGI is $170,000 plus $65,000, which is $235,000. With that same $200,000 limit, the excess is $235,000 minus $200,000, which is $35,000.

Now Walt compares two amounts. His net investment income is $65,000. His excess is $35,000. The smaller one is $35,000. He multiplies $35,000 by 3.8 percent. That is $1,330. So Walt owes $1,330 in this tax, on top of his regular income tax. Notice he did not pay on the whole $65,000. Only on the part that crossed the line. The tax would be $2,470 if it hit all of it, and it does not.

Where it goes wrong

A neighbor of mine once assumed that only rich investors ever see this tax. Then he sold a business interest and learned the hard way. The first trap is timing. One large sale can lift your MAGI over the limit for a single year, even if your normal income is modest. Selling a house, a farm, or a business can do exactly that.

The second trap is a wrong guess about what counts. People often think rental income is safe because it feels like work. Sometimes it is, and sometimes it is not. Whether it is subject to the tax depends on how involved you are and how the activity is classed. The Form 8960 instructions walk through this, and they are worth reading slowly.

The third trap is estimated tax. This surtax is not taken out of a paycheck. If a big gain is coming, the taxpayer may need to make estimated payments, or may face an underpayment penalty. The IRS describes estimated tax on its own pages.

The last trap is forgetting that the limit is not indexed. The statute fixes it, so as pay and asset values rise over the years, more households may cross it. Check your numbers each year. Do not lean on last year's answer.

Questions to answer before you leave this page

Have you looked at line 11 of your Form 1040 to see your adjusted gross income, and do you know your filing status limit? Are you planning to sell a home, a rental, a business, or a block of shares this year, and have you added that gain to your income to see where it lands? Do you know which of your income counts as net investment income and which does not? Have you read the Form 8960 instructions on irs.gov, or asked a tax professional to walk through your own case? And if you do owe, have you thought about whether estimated payments are needed so there is no surprise at filing time?