“I made a lot more money this year than last year. Will I owe a big bill to the IRS?” If that’s the question you typed into the search bar at 11pm, the honest answer is: probably yes, and probably more than you think.
Interest. A bonus. There’s 1099 income on the side, maybe one partner is carrying in their own paycheck. It’s all good news, and it all has the power to push you to a place where your withholding will never be able to handle it.
The rest of this post follows an imaginary but very ordinary reader. You could call them someone in their late 20s who had a comfortable W-2 salary last year and will make a significantly higher total this year thanks to a promotion and additional freelancing.
Their W-4s haven’t been touched in years. Everything that goes wrong for them also goes wrong for many people in their 20s and 30s. Let’s go over it.
Increase is Not a Problem. Untouched W-4
Our new high-income employee assumes his employer handles taxes correctly. Payroll subtracts something from every check. It shows up on the pay slip. Case closed, right?
Not really. The W-4 tells your employer how to withhold based on the picture you provide on the day you fill it out. If that day was a few years ago, a day when you made noticeably less money, the form still assumed a version of your life that no longer existed. Payroll systems don’t magically know when you got promoted, got a second job, or opened a Shopify store on the weekends.
The move no one talks about is boring and free: Get your latest pay stub, enter the numbers into the IRS Tax Withholding Estimator, and update your W-4. Do it once a year. Do this when your income varies by more than a few thousand dollars. If our reader had done this in the middle of the year, they would have caught a meaningful shortfall before it turned into an April surprise.
This Side Hustle Has Its Own Tax and No One Withheld For It
Let’s turn to our reader. Let’s say some of this new income came from freelance design work paid through 1099s.
On the W-2 side, Social Security and Medicare are automatically disabled and the employer covers the half. On the 1099 side, you are both the employee and the employer. This is the self-employment tax, which is a combined Social Security and Medicare tax that sits on top of regular income tax.
At a meaningful portion of net freelance income, the self-employment tier alone can reach four figures. Add federal income tax to the mix, and it’s easy for a side hustle to generate a profit. invoice that does not appear anywhere in any payment stud. The IRS wants this money in quarterly installments throughout the year, rather than in a single lump sum payment next April.
Two habits prevent this from spiraling:
- Scan a fixed percentage. Every time a customer pays you, move a healthy portion of it to a separate location. savings account. Pretend the money was never yours. When the quarterly deadlines hit in April, June, September and January, the cash is already there.
- Keep track of the interruptions as you progress. Software subscriptions, part of your phone bill, mileage to client meetings, home office. Waiting until March to reconstruct a year’s worth of expenses from memory is how people leave real money on the table.
401(k) Is the Best Leverage You Don’t Withdraw
This is where the story becomes more optimistic. Extra income creates extra taxes. It also creates extra room to move money to places the tax code rewards. The most powerful leverage for our reader is the workplace retirement plan.
IRS explained It states that employees can contribute up to $24,500 to a 401(k) and $7,500 to an IRA in 2026. Every pre-tax dollar you roll into a traditional 401(k) reduces this year’s taxable income by the same dollar. If our reader increases their contribution by a few percentage points, they will transfer thousands of dollars in taxable income to their future.
This is not a trick. This is the agreement that Congress wrote. The people who become truly wealthy in their 30s aren’t the ones with the biggest paychecks. They were the ones who noticed and pulled the levers before anyone else.
If You’re Renting, Check This Out. Read Twice If You Own It
Now let’s say our reader bought a condo last year in a state that imposes real income and property taxes. California, New York, New Jersey, Illinois: choose your taste.
Suddenly mortgage interest, property tax bills, and state income tax withholding start piling up in the detailed ledger.
For years, state and local tax deductions have made specification pointless for most young homeowners. This has changed. SALT cap Starting in 2025, it jumps from $10,000 to $40,000, increasing slightly each year until 2029.
For someone with a significant state income tax bill and a property tax bill on top of that, that limit was a real money sticking point. Not so now.
This doesn’t mean everyone needs to elaborate. The standard deduction is still higher for many filers. But if you’re a homeowner in a high-tax state and have been on autopilot since 2018, this is the year you’ll actually be running the numbers. Don’t take the standard deduction because you always have.
When Should You Hire Someone?
Our reader now has a W-2, 1099 with quarterly estimated payments, mortgage, government return, and 401(k) contributions they may want to increase before December 31st. This is the moment in TurboTax where doing it yourself stops being a sign of frugality and starts being a way to end up overpaying by hundreds or thousands of dollars.\
You don’t need a full-time accountant. You need to have a conversation once a year with someone who does this for a living. A good tax professional will find deductions you didn’t know existed, tell you whether the S-corp election makes sense from a side income perspective, and flag anything on your state return that a national software package poorly addresses. For example, a company in California: Robert Hall and Partners It builds strategy around specific rules of the state that national instruments tend to treat as an afterthought.
Tricky test: If your return this year includes any two of the items in the list below, get help.
- Self-employment income. Even a few thousand dollars in a 1099 job changes the shape of the return.
- An interstate move. Two half-year returns, two sets of rules, one very complicated piece of software.
- Buying or selling a home. Closing documents include deductions that people routinely overlook.
- Equity compensation. RSUs, ISOs, and ESPPs each come with their own tax landmines.
- A significant revenue increase. The new bracket is the phasing out of credits you used to claim and often your first exposure to estimated taxes.
One Afternoon Beats April Panic
Let’s get back to the reader we started with. If they update their W-4 tonight, open a savings package for freelancer money, and increase their 401(k) contributions by a few percentage points before the last paycheck of the year, they’ll have rewritten their April results.
No need for new income. There is no rush. I only paid attention one afternoon.
The goal is to make more money. Storing more is a separate skill. No one teaches this in school, and no one at your job will knock on your desk to remind you. But the levers are all there, in plain sight, waiting for the version of you to decide this year will pull them.
Photo: Markus Winkler: Unsplash
