Paying Tax On Side Income Nobody Withheld

The first year I made money outside a paycheck, I made about $11,000 doing freelance design work on nights and weekends. I set aside none of it.

In April I owed roughly $3,800 I did not have. I paid it on a credit card charging 21 per cent, which is a sentence I would like very much to take back.

Why nothing was withheld

When you are paid on a W-2, your employer withholds income tax from every paycheck and sends it in for you. It also pays half of your Social Security and Medicare tax and takes the other half out of your pay, which is why those lines are on the stub.

When you are paid as a contractor, or you sell things, or you rent a room, nobody does any of that. The money arrives whole.

So does the bill, eleven months later, with an extra piece attached.

The piece people have not heard of

Self employment tax is Social Security and Medicare charged on money you earned working for yourself. As an employee you pay half and your employer pays half. Working for yourself, you are both halves.

The combined rate is 15.3 per cent, and it applies to 92.35 per cent of your net self employment earnings rather than the full amount. The Social Security portion stops above an annual income ceiling that gets reset every year. The Medicare portion does not stop.

Run $18,000 of net side income through it. 92.35 per cent of $18,000 is $16,623. 15.3 per cent of $16,623 is $2,543.

Then income tax on top

You also owe ordinary income tax on that money, at whatever your marginal rate is, because side income stacks on top of the salary you already have. If your job already put you in a 22 per cent bracket, the side income starts there.

One thing works in your favour. You get to deduct half of the self employment tax when working out the income your tax is calculated on. Half of $2,543 is $1,272, so $18,000 minus $1,272 leaves $16,728.

$16,728 at an illustrative 22 per cent is $3,680.

$2,543 plus $3,680 is $6,223 on $18,000 of income, which is 34.6 per cent.

Which is why the common advice is to set aside 30 per cent, and why 30 per cent should be your floor rather than your target. If you live somewhere with a state income tax, or a city one, add that on top.

What counts, and what the forms will not tell you

You owe tax on the income whether or not a form ever arrives. A client who paid you $2,400 may send a 1099-NEC. A client who paid you $400 probably will not. Both amounts belong on the return.

Payment apps and online marketplaces report on their own schedules, under reporting thresholds that have been changed and delayed more than once in recent years. So the arrival of a form is not the definition of taxable income, and the absence of one is not an exemption. Your own records are the definition.

Which means keeping them. A spreadsheet with four columns, date, client, amount and what it was for, takes roughly ninety seconds a week and turns the following March from an archaeology project into a sum.

The quarterly part

The US system runs pay as you go. Tax is due as income is earned, not in one lump the following spring. For employees, withholding handles that invisibly every two weeks.

For everyone else there are estimated tax payments, usually four of them across the year. The due dates are published in the IRS instructions each year and they are not evenly spaced, which catches out roughly everybody in their first year.

If you come up short across the year, you can owe an underpayment penalty even when you pay the entire balance on time in April. The penalty is calculated like interest, charged on how short you were and for how long you were short, at a rate the IRS sets and updates.

Two ways to stay clear of it

• Pay estimates directly. IRS Direct Pay and EFTPS on irs.gov both take a bank transfer in about three minutes, four times a year, based on what you expect to owe.
• Or raise the withholding at your day job. File a new W-4 asking for extra dollars taken from each paycheck. Withholding is generally treated as having been paid evenly across the year no matter when it actually happened, which is genuinely useful if you notice the problem in October.
• Either way, know that the tax code contains safe harbour rules that protect you from the penalty if you pay at least a set share of the prior year's tax or of the current year's. The exact percentages vary by income level and are set in the code, so read the current year instructions rather than a number somebody quoted you.

The account that fixes this permanently

Open a second savings account at a bank you do not have a debit card for. Every time a client pays, move 30 per cent of the payment across the same day, before it lands in the checking account you spend from.

A $4,000 invoice means $1,200 moves and $2,800 stays. You will hate it in month one and forget about it by month four.

Do not think of the balance in that account as a cushion. It is the tax bill, sitting there early, and treating it as anything else is how the credit card story starts.

Expenses are the other lever

Self employment tax and income tax both get calculated on net income, which is revenue minus legitimate business expenses. Lowering the net lowers both.

Software subscriptions, the accountant's fee, the business share of your phone bill, mileage driven for the work, a portion of home costs if you genuinely qualify for the home office deduction as a self employed person. Keep the records as you go, because reconstructing a year of receipts in March is how people end up guessing, and guessing is how they end up under audit.

Do this

Add up what your side income has been so far this year. Multiply it by 0.30. If that money is not sitting somewhere separate right now, move what you can today and set the transfer rule for every payment from here.

Then find the next estimated payment deadline in the current year instructions and put it in your calendar with a reminder a week out.

The first year I did this properly, April was the most boring month of my financial life, and boring turns out to be the whole point.