You finished your tax return expecting a refund.

Instead, you owe the IRS.

Or maybe you knew you’d owe something—but the bill is thousands of dollars more than you expected.

The first question is usually:

What happened?

A larger-than-expected tax bill doesn’t necessarily mean your return was prepared incorrectly. Often, something changed during the year that caused you to have more taxable income, less withholding, or insufficient estimated tax payments.

Here are some of the most common reasons taxpayers end up owing more than they expected—and what you can do to avoid the same surprise next year.

1. Not Enough Tax Was Withheld From Your Paycheck

One of the most common reasons for an unexpected tax bill is straightforward:

You didn’t pay enough tax throughout the year.

Employees generally have federal and Wisconsin income taxes withheld from their paychecks.

But withholding is an estimate.

If too little was withheld relative to your actual tax liability, you’ll generally need to make up the difference when you file.

Several things can cause withholding to fall short:

• Changing jobs
• Receiving a raise
• Receiving bonuses
• Working multiple jobs
• Incorrect withholding elections
• Changes in household income
• A spouse returning to work
• Significant income outside your job

This is particularly common in households with two working spouses.

Each employer may withhold based primarily on the information available for that particular job. Without proper adjustments, the combined household income can produce a larger tax liability than expected.

2. You Started Freelancing or Earning 1099 Income

Maybe you made an extra $15,000 doing consulting work.

Or started a side business.

Or began receiving income as an independent contractor.

Unlike a traditional paycheck, taxes generally aren’t automatically withheld from payments you receive as a self-employed worker.

And there’s another potential cost:

Self-employment tax.

Self-employed individuals may owe Social Security and Medicare taxes in addition to federal and Wisconsin income taxes.

So if you received $30,000 of 1099 income and treated the entire $30,000 as spendable money, you could be in for a surprise at tax time.

Related: Self-Employed in Wisconsin? Here’s How Much You Should Set Aside for Taxes

3. Your Income Increased

Making more money is generally a good problem to have.

But it can change your tax situation.

Perhaps you:

• Received a substantial raise
• Earned a large bonus
• Changed to a higher-paying job
• Had an unusually profitable business year
• Started earning investment income
• Had a spouse return to work

The United States uses a progressive income-tax system, so moving into a higher tax bracket doesn’t mean all your income suddenly gets taxed at the higher rate.

But additional income can increase your overall tax liability.

It can also affect other parts of your return, including eligibility for certain deductions and credits.

4. You Sold Investments

A good year in your brokerage account can sometimes create a not-so-good surprise on your tax return.

If you sell an investment for more than your cost basis, you may realize a capital gain.

Depending on how long you owned the investment and other factors, that gain may be taxable.

For example, suppose you bought an investment for:

$20,000

and later sold it for:

$50,000.

Ignoring other adjustments, you may have approximately:

$30,000 of capital gain.

If no taxes were withheld when the investment was sold, that gain could increase the amount you owe when filing.

This can become particularly significant after:

• Selling a concentrated stock position
• Rebalancing investments
• Exercising stock compensation
• Selling cryptocurrency
• Selling appreciated property

Investment decisions and tax decisions often overlap.

5. Your Mutual Fund Distributed Capital Gains

This one can be particularly confusing.

You might owe tax on an investment even though you didn’t personally sell it.

Certain mutual funds can distribute capital gains to shareholders.

Those distributions may create taxable income in a taxable brokerage account.

So when reviewing an unexpected tax bill, don’t only ask:

“What investments did I sell?”

Also review the tax documents issued by your investment accounts.

6. You Took Money From an IRA or 401(k)

Retirement-account withdrawals can create taxable income.

If you take money from a traditional IRA or pre-tax 401(k), some or all of the distribution may generally be subject to income tax.

Depending on your age and circumstances, additional taxes may also potentially apply to certain early distributions.

A common problem is insufficient withholding.

Suppose you withdraw:

$40,000 from an IRA

but have little or no federal or Wisconsin tax withheld.

You may receive most of that $40,000 in cash—but the distribution can still increase your taxable income.

The tax bill eventually catches up.

7. You Did a Roth Conversion

A Roth conversion is another situation where people sometimes misunderstand what’s happening.

You didn’t spend the money.

You simply moved it from one retirement account to another.

So why did your tax bill increase?

Because moving pre-tax money from a traditional retirement account to a Roth account generally creates taxable income in the year of conversion.

A $50,000 taxable Roth conversion can potentially add approximately $50,000 to your income even though the money remains invested for retirement.

That’s why Roth conversions should generally be evaluated before they’re completed, not discovered while preparing the return.

Related: Should You Do a Roth Conversion? The Tax Questions to Answer First

8. Your Social Security Became More Taxable

Wisconsin generally doesn’t tax Social Security benefits, but federal taxes are different.

Depending on your income, up to 85% of Social Security benefits may be included in federal taxable income.

This can create a surprising interaction.

Maybe you:

• Took a larger IRA withdrawal
• Realized capital gains
• Completed a Roth conversion
• Started receiving pension income
• Earned more investment income

That additional income could potentially cause more of your Social Security benefits to become federally taxable.

So the tax effect can be larger than simply looking at the new income by itself.

Related: What Happens to Your Taxes When You Retire in Wisconsin?

9. You Received a Bonus

Bonuses can cause confusion because the amount withheld from a bonus isn’t necessarily the same as the amount you’ll ultimately owe because of that income.

Your final tax liability is determined based on your overall tax return.

So even though taxes were withheld from your bonus, the withholding may not perfectly match the additional tax ultimately generated by your total income.

A large bonus can therefore contribute to an unexpected balance due.

10. You Lost a Tax Credit or Deduction

Sometimes your tax bill goes up even though your income didn’t change dramatically.

Why?

You may no longer qualify for a tax benefit you received previously.

Changes can happen because:

• Your income increased
• A child no longer qualifies for a particular benefit
• Your dependent situation changed
• Education expenses changed
• Your filing status changed
• Your circumstances no longer meet the requirements for a credit or deduction

This is why comparing this year’s return with last year’s can be so useful.

Don’t only look at the refund.

Look at what changed on the return itself.

Your Refund Isn’t Your Tax Bill

This is one of the most important tax concepts to understand.

Suppose Person A receives a:

$5,000 refund

and Person B owes:

$1,000.

That doesn’t necessarily mean Person A paid less tax.

The refund or balance due primarily tells you the difference between:

Your total tax liability

and

How much you already paid during the year.

Think of it like paying a restaurant bill.

If your bill is $80 and you already paid $100, you get $20 back.

If your bill is $80 and you only paid $60, you owe another $20.

The refund doesn’t tell you how expensive dinner was.

Likewise, a tax refund by itself doesn’t tell you whether your taxes were high or low.

Compare Total Tax, Not Just Your Refund

If you’re trying to understand why this year feels so different, pull out your previous return.

Compare:

• Total income
• Adjusted gross income
• Taxable income
• Total tax
• Federal withholding
• Estimated payments
• Credits
• Capital gains
• Business income
• Retirement distributions

That comparison can often reveal the answer quickly.

For example:

Last year

Total tax: $18,000
Taxes paid during year: $20,000
Refund: $2,000

This year

Total tax: $20,000
Taxes paid during year: $17,000
Amount owed: $3,000

Your experience changed from a $2,000 refund to owing $3,000.

That feels like a $5,000 swing.

But your actual tax liability only increased $2,000.

The remaining difference came from paying less throughout the year.

That’s an important distinction because the solution may be to adjust your payments—not necessarily to find more deductions.

What Should You Do If You Owe Taxes?

First, determine why you owe.

Don’t immediately assume the answer is:

“I need more deductions.”

Maybe you simply need to adjust withholding.

Or make estimated payments.

Or account for investment income.

Or plan ahead for retirement distributions.

Once you’ve identified the cause, you can determine what should change.

Don’t Ignore the Tax Bill

If you owe taxes and can’t pay the entire balance immediately, don’t ignore the return or avoid filing solely because you can’t pay.

Failure to file and failure to pay can create different consequences.

Generally, filing an accurate return on time and addressing the payment issue is preferable to simply doing nothing.

Depending on the circumstances, payment options may be available through the IRS and Wisconsin Department of Revenue.

How Do I Avoid Owing Next Year?

This is where tax planning comes in.

Once we understand why you owe, we can look forward.

Possible solutions could include:

• Updating your W-4
• Increasing federal withholding
• Increasing Wisconsin withholding
• Making estimated tax payments
• Increasing withholding from retirement distributions
• Setting aside taxes from self-employment income
• Projecting taxes before selling investments
• Reviewing Roth conversions before completing them
• Running a mid-year tax projection
• Running another projection before year-end

The right solution depends on what caused the problem.

The Best Time to Find a Tax Surprise Is Before April

Imagine discovering in October that you’re on track to owe an additional $8,000.

That’s useful information.

You still have time to understand what’s happening and evaluate your options.

Discovering the same $8,000 when your return is being prepared gives you fewer choices.

That’s one of the biggest differences between tax preparation and tax planning.

Tax preparation tells you what happened.

Tax planning gives you time to respond.

Why Do I Owe Taxes This Year?

If your tax bill was much higher than expected, don’t settle for:

“That’s just what the software says.”

You should understand what changed.

At La Crosse Tax, we help individuals and business owners prepare their tax returns and understand the reasons behind the numbers.

And if something caused an unexpected tax bill this year, we can help determine whether your withholding, estimated payments, or tax strategy should change going forward.

Thinking about a Roth conversion this year?