The United States has a pay-as-you-go tax system. Employees handle this automatically through withholding. But if you’re self-employed, receive investment income, run a pass-through business, or have any income not subject to withholding, you’re responsible for sending money to the IRS yourself — on a quarterly schedule that most people only think about when they miss it.

Who Needs to Make Estimated Payments

You’re generally required to make estimated tax payments if you expect to owe at least $1,000 in federal tax after subtracting withholding and refundable credits, and your withholding and credits will cover less than the smaller of:

• 90% of the tax you’ll owe for the current year, or

• 100% of the tax you owed for the prior year (110% if your prior-year AGI exceeded $150,000)

This threshold — covering 100% or 110% of last year’s tax — is the foundation of the “safe harbor” rule. If you pay estimated taxes equal to your full prior-year tax liability, you won’t owe an underpayment penalty even if your actual tax for the current year turns out to be higher.

Who typically needs to pay:

• Self-employed individuals and sole proprietors

• S-Corp shareholders and LLC members with pass-through income

• Real estate investors with passive income

• Investors with significant capital gains, dividends, or interest income

• People who received a large bonus and don’t have sufficient withholding

• Retirees with pension, IRA, or Social Security income and limited withholding

The Quarterly Due Dates

Estimated taxes are due four times per year, but not in equal quarterly intervals. The IRS schedule is:

• Q1 (January 1 – March 31): Due April 15

• Q2 (April 1 – May 31): Due June 16

• Q3 (June 1 – August 31): Due September 15

• Q4 (September 1 – December 31): Due January 15 of the following year

Missing a payment or underpaying a specific quarter can trigger an underpayment penalty even if you fully catch up by year-end. The penalty is calculated quarter by quarter, not on an annual basis. Paying everything in Q4 doesn’t undo a shortfall in Q1 through Q3.

The Safe Harbor Calculation — and Why It Matters

The most reliable way to avoid underpayment penalties is to use the prior-year safe harbor: pay at least 100% of last year’s total tax liability in estimated payments (or 110% if your prior-year AGI exceeded $150,000).

Example: If you owed $60,000 in total federal income tax in 2025 and your AGI exceeded $150,000, you need to pay at least $66,000 in estimated taxes for 2026 ($60,000 × 110%) to avoid penalties — regardless of what you actually owe when you file.

This approach is particularly useful when income is variable. If you had a great year in 2025 but 2026 is soft, you’re still protected by last year’s numbers. Your accountant can calculate the exact amount needed at the beginning of the year.

The 90% current-year safe harbor is more useful when your income drops significantly year-over-year. If you expect to owe $40,000 in 2026, you only need to pay $36,000 during the year to avoid penalties, even if you paid $66,000 the year before.

Common Mistakes That Lead to Penalties

Waiting until April to pay: Many people don’t think about estimated taxes until they file their return. By then, four quarterly deadlines have already passed, and the underpayment penalty for each quarter has already accrued.

Ignoring one-time income events: A business sale, large capital gain, inheritance distribution from an IRA, or settlement payment can create a sudden, large tax liability that your standard payment pattern doesn’t cover. These events require an extra payment or adjustment in the quarter they occur.

Not accounting for self-employment tax: Estimated payments cover both income tax and self-employment tax (15.3% on the first $176,100 of net self-employment income in 2025, and 2.9% above that — verify current limits). Many new self-employed people underestimate this and end up with a large balance due.

Relying on last year’s pattern when income jumped: If you had a significantly better year than the prior one, the safe harbor protects you from the penalty — but you’ll still owe the actual tax when you file. Planning for the cash outflow is separate from planning to avoid the penalty.

Frequently Asked Questions

Q: What is the underpayment penalty rate?

A: The IRS penalty rate for underpaid estimated taxes is the federal short-term interest rate plus 3 percentage points — it’s not a fixed percentage. It fluctuates. In recent years it has been in the 7–8% range. (Verify the current rate with the IRS or your tax advisor.)

Q: Can I avoid the penalty if I had very little income at the beginning of the year?

A: Yes. The annualized income installment method (Form 2210, Schedule AI) allows you to calculate estimated tax based on income earned through each period rather than spreading your tax evenly. If your income is concentrated later in the year, this can reduce or eliminate underpayment penalties for earlier quarters.

Q: Can I increase withholding from a job to cover estimated taxes on other income?

A: Yes, and this is often the simplest solution. You can file a new W-4 requesting additional withholding from your employer. Since withholding is treated as paid evenly throughout the year for IRS purposes, this can cure underpayments in earlier quarters even if the withholding happens late in the year.

Q: Do I need to make state estimated payments too?

A: Usually, yes. Most states with an income tax have their own estimated payment requirements. Texas has no state income tax, so this is less of a concern for Texans — but if you have income sourced to other states, those states may still require payments.

Estimated taxes are manageable once you understand the system. The penalty for getting it wrong is annoying but not catastrophic — but the surprise balance due at filing can cause real cash flow problems if you haven’t been setting money aside.

If you’d like to apply this to your situation, the team at Molen & Associates is here to help. Schedule a consultation at molentax.com.