Idaho Quarterly Tax Calculator
Calculate your estimated quarterly tax payments for federal and Idaho state taxes. Designed for self-employed individuals, freelancers, and independent contractors.
ID State Tax: Flat 5.8%
Quarterly Payment Amount
$6,671
Per quarter (4 remaining)
Annual Tax Breakdown
2026 Payment Schedule
Jan 1 - Mar 31
Due: April 15, 2026
$6,671
Apr 1 - May 31
Due: June 15, 2026
$6,671
Jun 1 - Aug 31
Due: September 15, 2026
$6,671
Sep 1 - Dec 31
Due: January 15, 2027
$6,671
Don't miss your quarterly payments!
The IRS may charge penalties and interest if you underpay or pay late. Consider setting up automatic payments or calendar reminders.
Idaho Quarterly Tax Highlights
Idaho has a flat 5.8% income tax rate
Recently converted from progressive to flat tax
Use Form 51 for quarterly payments
Simple calculation with single rate
Idaho Quarterly Tax FAQ
What is Idaho's income tax rate?
Idaho has a flat 5.8% income tax rate. The state recently converted from a progressive tax system to a flat tax, simplifying calculations for all taxpayers.
Idaho Estimated Quarterly Tax Payments for Self-Employed Workers in 2026
Self-employed workers in Idaho face two tax obligations: federal estimated taxes filed with the IRS and state estimated taxes filed with the Idaho State Tax Commission. Idaho imposes a flat 5.8% income tax rate on all taxable income. If you expect to owe $1,000 or more in Idaho state income tax after withholding and credits, you must make quarterly estimated payments using Form 51.
Idaho recently converted from a progressive system (with rates up to 6%) to a flat 5.8% rate, simplifying calculations for all taxpayers. The state conforms closely to federal tax definitions.
| Tax Layer | Rate / Range | Filed With | Form |
|---|---|---|---|
| Federal income tax | 10% – 37% | IRS | 1040-ES |
| Self-employment tax | 15.3% | IRS | 1040-ES / SE |
| Idaho state income tax | 5.8% | Idaho State Tax Commission | Form 51 |
How Idaho's Flat 5.8% Income Tax Affects Your Quarterly Payments
Idaho uses a flat tax rate of 5.8%, which simplifies quarterly tax calculations. Regardless of income level, every dollar of taxable income is taxed at the same rate. This makes it straightforward to estimate your state quarterly payments — simply multiply your projected net self-employment income by 5.8% and divide by four.
For a single self-employed worker in Idaho earning $100,000 in net self-employment income, the estimated annual tax breakdown is:
| Tax Component | Estimated Amount | Calculation Basis |
|---|---|---|
| Federal income tax | ~$11,600 | After $15,700 standard deduction, 2026 brackets |
| Self-employment tax | ~$14,130 | 15.3% on 92.35% of net earnings |
| Idaho state income tax | ~$5,800 | 5.8% flat rate |
| Total annual tax | ~$31,530 | |
| Quarterly payment | ~$7,883 | Total / 4 quarters |
State payments can be made online through the Idaho State Tax Commission portal at tax.idaho.gov, by mail with a Form 51 voucher, or via electronic funds transfer where available.
Federal Self-Employment Tax and Quarterly Due Dates
All self-employed workers must pay federal self-employment (SE) tax of 15.3% on 92.35% of net earnings. This consists of 12.4% for Social Security (on earnings up to $184,500 in 2026) and 2.9% for Medicare (no cap). An additional 0.9% Medicare surtax applies to earnings above $200,000 (single filers).
Both Idaho and federal estimated tax payments follow the same quarterly schedule:
| Quarter | Income Period | Due Date |
|---|---|---|
| Q1 | January 1 – March 31 | April 15, 2026 |
| Q2 | April 1 – May 31 | June 15, 2026 |
| Q3 | June 1 – August 31 | September 15, 2026 |
| Q4 | September 1 – December 31 | January 15, 2027 |
To avoid underpayment penalties, pay at least 100% of your prior-year tax liability (or 110% if your AGI exceeds $150,000) spread across four equal payments, or at least 90% of your current-year tax. You can deduct 50% of your self-employment tax from your adjusted gross income, reducing both your federal and Idaho taxable income.
Related Calculators
Official References
This calculator uses current federal and Idaho tax rates and schedules:
- IRS Estimated Tax Guidelines
Federal quarterly tax requirements and Form 1040-ES
- Idaho State Tax Commission
Official Idaho tax authority
- IRS Self-Employment Tax
Social Security and Medicare tax information
This calculator provides estimates based on 2026 tax rates. Your actual tax liability may vary based on deductions, credits, and other factors. Consult a tax professional for personalized advice.