2026 Tax Penalties and Interest: IRS + Colorado

Two numbers decide how much a late tax bill really costs: the 5% monthly failure-to-file penalty and the 0.5% monthly failure-to-pay penalty. Get them wrong and a manageable balance can grow by 25% before you act. This alert covers the federal rules that reach every taxpayer, plus the Colorado Department of Revenue charges that land on Denver and Littleton business owners on top.

The people who get hurt most are pass-through owners and small-business owners who file late, underpay their estimates, or assume an extension buys more time to pay. It does not. An extension moves your filing deadline, not your payment deadline, so interest and the failure-to-pay penalty start running from the original spring due date.

2026 Tax Penalties and Interest at a Glance

Here is how the federal and Colorado charges compare for 2026. Federal penalties come from the Internal Revenue Code; Colorado’s come from state statute and a rate reset each January.

What Is the Failure-to-File Penalty Rate for 2026?

The failure-to-file penalty is 5% of the unpaid tax for each month or part of a month your return is late, up to a maximum of 25%. It is the most expensive of the two late penalties, which is why filing on time matters even when you cannot pay the full balance. A return more than 60 days late carries a minimum penalty of the lesser of $525 or 100% of the tax owed.

The penalty applies to the balance still owed, so filing an accurate return promptly stops the 5% clock even if a payment plan handles the rest. The IRS confirms the arithmetic in its published guidance (IRS: Failure to File Penalty).

“If both a Failure to Pay and a Failure to File Penalty are applied in the same month, the Failure to File Penalty is reduced by the amount of the Failure to Pay Penalty applied in that month.” — Internal Revenue Service, Failure to File Penalty

What Is the IRS Failure-to-Pay Penalty Rate?

The failure-to-pay penalty is 0.5% of the unpaid tax for each month or part of a month the tax stays unpaid, capped at 25%. It is one-tenth the monthly rate of the failure-to-file penalty, which is the core reason tax advisors tell clients to file on time and pay what they can. Interest under IRC §6621 accrues on top of the penalty.

If you set up an approved installment agreement and your return was filed on time, the failure-to-pay rate drops to 0.25% per month for the months the agreement is in effect. That is a straightforward, statutory way to cut the penalty in half while you pay the balance down.

How Does the Penalty Overlap Rule Work?

When both penalties apply in the same month, they do not simply stack to 5.5%. The failure-to-file penalty is reduced by the failure-to-pay penalty, so the combined charge is 5% per month: 4.5% for filing late plus 0.5% for paying late. Take a $10,000 unpaid balance filed and paid three months late:

1. Failure-to-file portion: 4.5% x 3 months x $10,000 = $1,350.
2. Failure-to-pay portion: 0.5% x 3 months x $10,000 = $150.
3. Combined penalty before interest: $1,500, or 15% of the balance in three months.

What this means for you: the file-late penalty does the heavy lifting. Filing on time and paying late on that same $10,000 would have cost $150 in penalty over three months instead of $1,500.

What Are the IRS Interest Rates for 2026?

For individuals, the IRS underpayment and overpayment interest rate is 7% for the first quarter of 2026, 6% for the second quarter, and 7% for the third quarter, compounded daily. Large corporate underpayments run higher, at 9% in Q1, 8% in Q2, and 9% in Q3. The rate is the federal short-term rate plus three percentage points and is set every quarter, so verify the current figure before you rely on it.

Interest is separate from penalties. It runs from the original due date until the balance is paid in full, and it applies to unpaid penalties as well as unpaid tax. The IRS publishes each quarter’s figure in its quarterly interest rates table.

How Do Estimated-Tax Safe Harbors Protect You?

You avoid the estimated-tax underpayment penalty by meeting a safe harbor: pay at least 90% of your current-year tax, or 100% of your prior-year tax through withholding and quarterly estimates. If your prior-year adjusted gross income was more than $150,000, the prior-year threshold rises to 110%.

What this means for you: pass-through owners with uneven income can lock in the prior-year safe harbor early, then true up in the fourth quarter. That keeps the underpayment penalty, charged at the same rate as underpayment interest, off the table even in a strong year. Individuals with W-2 income can adjust their Form W-4 withholding to close the same gap, and our individual tax planning team runs those projections before year-end.

Pass-Through Entity Late-Filing Penalty: S Corporations and Partnerships

For 2026 federal tax returns (returns required to be filed in 2026), the IRS increased the late-filing penalty for pass-through entities to $255 per owner per month, or part of a month, up to a maximum of 12 months. This applies even if the entity owes no income tax, because partnerships and S corporations are generally pass-through entities. The IRS may waive the penalty if the entity demonstrates reasonable cause.

Certain domestic partnerships may qualify for administrative relief under Revenue Procedure 84-35 if all of the following are met:

• The partnership has 10 or fewer partners.
• Each partner is an individual (other than a nonresident alien) or the estate of a deceased partner.
• Each partner timely reports their distributive share of partnership income, deductions, and credits on their own return.
• Allocations are proportional among partners.

Colorado Penalties and Interest: What CO DOR Charges

Colorado adds its own layer on top of the federal charges. For 2026, the Colorado Department of Revenue applies an 11% annual interest rate on unpaid tax, down from 12% in 2025, with a discounted 8% rate for taxpayers who pay before a notice of deficiency or within 30 days of one. The rate is reset each January.

The Colorado late-payment penalty is the greater of $5 or 5% of the unpaid tax, plus an additional 0.5% for each month the tax remains unpaid, not to exceed 12% total (C.R.S. §39-22-621). For a Denver or Littleton business already facing federal penalties, the combined federal-plus-state exposure is what makes a late season expensive. Paying promptly to earn Colorado’s discounted 8% rate is a concrete reason to act early, and our state and local tax team handles Colorado DOR notices and multistate filings.

Why Do I Owe a Penalty and Interest, and What Can I Do About It?

You owe both because they answer different questions: the penalty is charged for filing or paying late, and interest is the time-value charge on money the government was owed. You can often reduce penalties, but interest is statutory and rarely removed. The practical playbook is to file immediately, pay what you can to shrink the base both charges run on, and then request relief.

Three levers matter most: first-time penalty abatement if your recent compliance record is clean, an installment agreement to cut the failure-to-pay rate to 0.25%, and reasonable-cause relief when events outside your control caused the delay. A CPA can file these requests and, when a notice escalates, handle IRS and state representation on your behalf. The pandemic-era automatic waivers have ended, and the IRS is phasing in an Automatic Exemption from Penalty (AEP) program starting in summer 2026 that replaces first-time abatement for eligible 2025 returns and 2026 quarterly filings (see the FAQ below). Where AEP does not apply, relief is requested case by case through reasonable cause.

Frequently Asked Questions

How does an installment agreement affect IRS penalties?

An approved installment agreement cuts the failure-to-pay penalty from 0.5% to 0.25% per month for the months the agreement is in effect, as long as your return was filed on time. It does not stop interest, which continues to accrue on the unpaid balance until it is paid in full.

Can the IRS remove interest along with penalties?

Usually not. Interest is set by statute and is generally only abated when it results from an IRS error or unreasonable delay. Penalties are more often reduced or removed, but reducing the underlying tax and penalties is the main way to shrink the interest that runs on top of them.

What is first-time penalty abatement?

First-time penalty abatement is IRS relief that can remove failure-to-file and failure-to-pay penalties if you have a clean compliance history, meaning no penalties for the prior three years, all required returns filed, and any balance paid or on a payment plan. It is requested per return and does not remove interest.

What happens if I miss the October 15 extended deadline?

If you filed an extension and miss the October 15 extended deadline, the 5% monthly failure-to-file penalty applies retroactively to your unpaid balance from the original spring due date. Pass-through entities such as partnerships and S corporations face the earlier September 15 extended deadline, so those returns are exposed sooner.

Does the IRS automatic penalty relief apply to me in 2026?

The IRS is phasing in a new program called Automatic Exemption from Penalty (AEP), starting in summer 2026, that replaces the older First-Time Abate (FTA) process. AEP applies to eligible 2025 tax-year returns and 2026 quarterly returns, and to later years. If you file or pay late but have timely filed and paid for the prior three years (or twelve consecutive quarters), the IRS will not assess a failure-to-file, failure-to-pay, or failure-to-deposit penalty in the first place, and it sends a notice confirming the relief, with no request needed. That is the key difference from FTA, which required you to ask and assessed the penalty before removing it. Eligible returns include Forms 1040, 1065, and 1120, the 940 through 945 series, and Form CT-1. If you receive a notice showing a penalty but believe you qualified, contact the IRS or your CPA.

Facing a penalty notice or worried about your estimates? Schedule a free tax readiness check with our Denver-area tax team to review your 2026 exposure and build a plan to reduce it. Start with WhippleWood’s business tax planning or contact our team to book a consultation.