Definition
A balance due — also called 'tax due' or 'owing in April' — occurs when your total federal income tax for the year exceeds what was withheld from your paychecks. You pay the difference when you file your tax return, by the April filing deadline.
Owing a small balance (under $1,000) is normal and not penalized. The IRS underpayment penalty kicks in when you owe $1,000 or more AND your withholding fell below safe harbor thresholds.
Common causes: two jobs where both employers withhold as if it's your only job, a working spouse in a higher combined bracket, freelance income without estimated payments, or a large investment gain or bonus late in the year.
How this affects your W-4
The calculator shows the 'Projected Tax Due' amount when your current withholding settings will result in under-withholding. The refund target tool lets you adjust Step 4c to either eliminate the balance entirely or reduce it to a manageable amount that stays below the $1,000 penalty threshold.
If the balance is $1,000 or more, check whether you're within safe harbor — if not, adjust Step 4c for remaining paychecks.
See how balance due affects your withholding
Use the free W-4 calculator to calculate your exact withholding with your specific situation.
Open the W-4 Calculator →Read the guide
Too Much or Too Little Tax Withheld? How to Tell and Fix Your W-4 (2026)
Signs, causes and W-4 fixes for withholding that is too high or too low, with a two-minute check.
How to Stop Owing Taxes at Tax Time: Fix Your W-4 (2026)
Owe the IRS every April? Why withholding falls short and which W-4 lines close the gap on your next paycheck.
Tax Refund vs. Adjusting Your W-4: How to Keep More Money Every Paycheck
The average refund is $3,100 — that's money that was yours all year. Here's how to decide whether a big refund is working for you or against you.
IRS Safe Harbor: How to Avoid Underpayment Penalties on Your W-4 (2026)
The IRS charges penalties when you underpay by too much. The safe harbor rules let you optimize your W-4 aggressively without triggering them.
Related terms
Underpayment Penalty
An IRS penalty charged when you owe more than $1,000 and your withholding falls below safe harbor thresholds.
Tax Refund
Money the IRS returns to you when your withholding exceeds your actual tax liability for the year.
Safe Harbor Rule
An IRS rule that protects you from underpayment penalties if your withholding meets either of two minimum thresholds.