Idaho is a flat-rate state with one twist at the bottom. The first $4,811 of single taxable income is taxed at zero percent, and everything above it is taxed at 5.3 percent. There are no brackets to climb, so the whole question for a reader is how much of the salary survives the standard deduction and the zero slice before the flat rate starts.
Enter your salary and filing status to see the Idaho line alongside federal tax and FICA.
Two subtractions before the rate applies
A single filer at $80,000 first subtracts the $16,100 single standard deduction, leaving $63,900 of taxable income. Then the zero-rate slice removes the first $4,811 of that, leaving $59,089 taxed at 5.3 percent. The state tax is therefore $3,131.72, not 5.3 percent of the full salary. Paid biweekly, that is about $120.45 per paycheck, and the effective rate on gross pay is about 3.91 percent.
Joint filers get a larger pair of subtractions: a $32,200 standard deduction and a $9,622 zero-rate threshold. At $80,000, joint taxable income is $47,800, the taxed portion is $38,178, and the state tax is $2,023.43, about $77.82 biweekly. The rate never changes between single and joint, the subtractions do all the work.
One labelling point matters here. The $4,811 single and $9,622 joint thresholds are labelled as the latest published 2025 thresholds, because the Tax Foundation January 2026 table carried the same thresholds with a note that 2026 inflation-adjusted widths were not available at publication. Do not read them as a confirmed 2026 indexed figure; read them as the threshold the calculator currently uses.
Why a flat rate still leaves a gap between marginal and effective rates
Readers sometimes assume a flat rate means marginal and effective rates are the same. They are not, while a deduction and a zero slice exist. The marginal rate on the last dollar is 5.3 percent, but the effective rate on gross pay is only 3.91 percent single, because $20,911 of the salary is never taxed at all. As pay rises, the effective rate creeps toward 5.3 percent but never quite reaches it, since the untaxed portion stays fixed in dollars.
A raise is simple to price. Every extra dollar of taxable income above the zero slice adds 5.3 cents of Idaho tax, at $80,000 or at higher incomes, with no threshold to cross. Source for the rate and deductions: Tax Foundation 2026 State Income Tax Rates and Brackets, with the zero-rate threshold labelled as above.
FAQs
Is Idaho really a flat-rate state?
Yes, at 5.3 percent above the zero-rate threshold. The zero slice makes the bottom of the schedule look progressive, but there is only one positive rate.
Why is the threshold described as a 2025 figure?
Because the Tax Foundation January 2026 table carried the same thresholds with a note that 2026 inflation-adjusted widths were not available at publication. The calculator uses those thresholds and labels them that way.
Does filing jointly change Idaho's rate?
No, the rate stays 5.3 percent. Joint filers get the larger $32,200 deduction and $9,622 zero slice, which is what lowers their tax on the same salary to $2,023.43 in this example.