How to Delay Taxes and Avoid Penalties on Non-W2 Income
For most taxpayers, paying income tax is simple: you earn a salary, your employer calculates the tax, and the money is withheld from your paycheck before it ever hits your bank account. You file a return in April merely to "settle up" any small differences.
However, in some years, your financial situation breaks this pattern. You might experience a massive spike in taxable income from a specific event—money that arrives "gross," without a single dime sent to the IRS. Common examples include:
Selling Real Estate: Selling a rental property, a vacation home, or even a primary residence (if the profit exceeds the exclusion limits) generates a large, one-time tax bill.
Liquidation for Large Purchases: Selling investments to fund a large expense (a down payment, a car purchase, etc) often triggers significant capital gains taxes.
Starting a Consulting Gig: Picking up freelance work or consulting contracts usually results in 1099 income, which—unlike a W-2 job—has zero taxes withheld automatically.
Performing a Roth Conversion: Moving funds from a Traditional IRA to a Roth IRA creates a massive, momentary spike in your taxable income for the year.
Taking Required Minimum Distributions (RMDs): Reaching age 73 or holding an inherited IRA often forces you to take taxable distributions whether you need the money or not.
These non-W2 income sources can double or triple your taxable income overnight. Because taxes are not automatically withheld from them, they create a sudden, invisible tax liability. And without any adjustments, the taxes being withheld from your paycheck will only cover your employment income, not these outside sources of income.
Can’t I wait until April to pay the taxes?
With non-W2 income sources, a common mistake is to assume that you can simply wait until tax season to pay the taxes due. You may even set aside some of the income in a savings account in anticipation of that future tax bill.
The reality is that the U.S. tax system operates on a "pay-as-you-go” basis, meaning the IRS expects to receive the tax payment roughly when you receive the income. If the taxes aren’t withheld automatically, the IRS generally requires you to file Form 1040-ES and make estimated payments four times a year on strict deadlines: April 15, June 15, September 15, and January 15.
If you fail to make these payments, the IRS considers them overdue. For example, if you sold your house in June but wait until the following April to pay the tax, the IRS views that payment as almost a year late. The IRS then charges an underpayment penalty¹, which acts like interest on a loan. The penalty rate fluctuates with interest rates, but assuming an 8% penalty, waiting until April to pay a $10,000 tax bill could cost you roughly $600 in non-deductible fines—essentially burning money. (It should also be noted that if the tax money was invested in the meantime and the markets did better than the penalty rate, you would end up coming out ahead and it would have been worth it to pay the penalty.)
Note: Even if you received the income late in the year (like a year-end bonus or a December home sale), the IRS assumes that you earned the income evenly throughout the year, and expects you to have made quarterly estimated tax payments over the course of the year. While it is possible to avoid the penalty by filing IRS Form 2210 to prove exactly when you earned the income, it is far simpler to use the withholding method described below to bypass that paperwork.
Can I somehow withhold the taxes instead?
In general, withholding taxes is almost always simpler than making quarterly payments. This is because the IRS treats any tax withheld as if it were paid evenly throughout the year, regardless of when it actually happened. If you withhold $10,000 in December, the IRS treats it as if you paid $2,500 in April, June, September, and January. In short, withholding retroactively voids any underpayment penalties.
Unfortunately, for many of these non-W2 income sources, withholding is either unavailable or financially unwise:
Selling Real Estate: Withholding is generally unavailable since title companies rarely withhold income tax from sales proceeds. You receive the gross cash amount, leaving you to handle the tax bill yourself.
Liquidation for Large Purchases: Withholding is unavailable because brokerages don’t automatically withhold capital gains tax from investment sales. You receive the full proceeds of the trade.
Starting a Consulting Gig: Withholding is unavailable because clients pay you the gross amount, and do not handle taxes for contractors.
Doing a Roth Conversion: Withholding is generally considered unwise since paying taxes from the conversion reduces the amount that makes it into the Roth, lowering your future tax-free growth.
The Result: You are often left with a large tax bill from these events and no easy way to withhold the necessary taxes from the income itself to cover it.
Thankfully, there is a way to satisfy the IRS and avoid underpayment penalties on these un-withhold-able income sources without having to make quarterly estimated tax payments. This withholding loophole allows you to effectively defer paying taxes on non-W2 income until April, and invest the taxes in the meantime.
The Withholding Loophole: Prior Year Tax Safe Harbor Rule
The Prior Year Tax Safe Harbor Rule allows you to pay a "baseline" amount of tax during the year (based on last year's income) while deferring the "excess" tax (generated by your new windfall) until April 15th, penalty-free. Under the rule, the IRS will not charge you a penalty as long as your total withholding for the year meets one of two criteria:
100% of last year's tax, if your adjusted gross income (AGI) last year was $150,000 or less.
110% of last year’s tax, if your adjusted gross income (AGI) last year was above $150,000.
This means you can avoid the whole mess - underpayment penalties, quarterly tax payments, impossible withholdings - as long as you make sure your total withholding for the year meets the criteria above.
Here are the steps you need to take to do this:
Step 1: Look at last year’s tax return: Find your Total Tax (line 24 on the 2025 Form 1040) and your AGI (line 11 on the 2025 Form 1040), it is on Line 11.
Find your Total Tax - on the 2025 Form 1040, it is on Line 24.
Find your AGI - on the 2025 Form 1040, it is on Line 11.
Step 2: Calculate your withholding target² for the current year:
If your AGI was $150k or below, your withholding target is simply last year’s Total Tax.
If your AGI was above $150k, your withholding target is your Total Tax * 110%.
Step 3: Check your current withholding: Look at your current paystubs or IRA distribution statements. Are you on track to have the target amount above withheld by December 31st? If not, what is your shortfall?
Step 4: Increase your withholding to bridge the gap: If you are looking at a shortfall, do one or more of the following:
If you’re employed, increase the withholding on your remaining paychecks to hit the target by Dec 31st.
If you are older than 59½, take an IRA distribution in the amount of the shortfall and withhold 100% of it.
If you are subject to an RMD from an IRA, withhold enough from the RMD to cover the shortfall.
If you are on social security, increase the voluntary withholding on your remaining benefits for the year.
If you receive a regular pension or annuity payout, increase your federal tax withholding to cover the shortfall.
Note: If you are married and filing jointly, the IRS treats your combined withholding as a single bucket. This means your spouse can also utilize any of the methods above to help cover the household shortfall.
By proactively adjusting your withholding to hit the Safe Harbor target, you neutralize the risk of underpayment penalties without the hassle of quarterly tax payments, and you get to hold onto the taxes on your non-W2 income until April, rather than sending them to the IRS prematurely. Just remember: come April 15th, that tax bill will come due, so ensure you have the cash set aside to pay it in full.
If your final tax bill (the total amount you owe when you file, after subtracting your withholding) is less than $1,000, the IRS will not charge you an underpayment penalty.
If last year was a massive windfall year, your "Last Year's Tax" target will be artificially high. In that scenario, the IRS offers an alternative safe harbor: you can avoid penalties by withholding at least 90% of this year's total tax. While harder to estimate since the year isn't over, this keeps your required withholding target much lower when last year’s income is artificially high.
