Idaho State Income Tax Calculator
This Idaho income tax calculator helps residents and employers estimate Idaho state income tax quickly and accurately. It supports standard or itemized deductions, common pre-tax contributions, optional credits, and an annual or per‑paycheck view. Built for clarity, speed, and accessibility.
Calculator
Results
Per‑Paycheck View
Data Source and Methodology
Authoritative data source: Idaho State Tax Commission — Individual Income Tax Rate Schedule (current flat rate). Reference: Individual Income Tax Rate Schedule (accessed September 2025).
Standard deduction levels align with federal 2024 amounts (IRS Rev. Proc. 2023-34). See IRS Rev. Proc. 2023‑34.
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
- Flat Idaho tax rate modeled at 5.8% for 2024.
- Idaho taxable income approximated from gross income minus common pre‑tax adjustments and chosen deduction method.
- Optional Idaho credits subtract directly from computed state tax.
The Formula Explained
Annual taxable income:
$$ \text{Taxable} = \max\!\big(0,\; G - R - H - D \big) $$
State tax before credits:
$$ T = r \times \text{Taxable} $$
Net state tax after credits:
$$ T_{\text{net}} = \max\!\big(0,\; T - C \big) $$
Effective rate on gross:
$$ \text{EffRate} = \frac{T_{\text{net}}}{G} $$
Per‑paycheck withholding (frequency p):
$$ T_{\text{pp}} = \frac{T_{\text{net}}}{p} $$
Where G = gross income, R = pre‑tax retirement, H = HSA, D = deduction (standard or itemized), r = Idaho flat rate, C = Idaho credits.
Glossary of Variables
- Annual Gross Income (G): Wages/salary before taxes or deductions.
- Pre‑tax Retirement (R): Traditional 401(k)/403(b)/457 employee contributions.
- HSA (H): Employee Health Savings Account contributions.
- Deduction (D): Standard (based on filing status) or your itemized total.
- Idaho Taxable Income: Amount subject to Idaho’s flat rate after adjustments.
- Idaho Credits (C): Any state credits that reduce tax owed.
- Idaho State Income Tax (T): Taxable × 5.8% (for 2024).
- Net Idaho State Tax (Tnet): State tax after credits (not below $0).
- Effective Idaho Tax Rate: Net Idaho tax divided by gross income.
- Per‑Paycheck: An even split of annual net tax across the selected pay periods.
How It Works: A Step‑by‑Step Example
Scenario: Single filer in 2024, $80,000 gross, $6,000 pre‑tax retirement, $2,000 HSA, Standard Deduction, no credits.
- Compute Taxable Income using the formula:
$$ \text{Taxable} = \max\big(0,\; 80{,}000 - 6{,}000 - 2{,}000 - 14{,}600\big) = 57{,}400 $$
- Apply Idaho flat rate 5.8%:
$$ T = 0.058 \times 57{,}400 = 3{,}329.20 $$
- No credits, so net tax is the same:
$$ T_{\text{net}} = 3{,}329.20 $$
- Effective rate on gross:
$$ \text{EffRate} = 3{,}329.20 / 80{,}000 = 4.16\% $$
- Per‑paycheck (Biweekly, 26): $3,329.20 / 26 ≈ $128.81
Frequently Asked Questions (FAQ)
Is Idaho’s income tax really flat?
Yes. For 2024 Idaho applies a flat 5.8% to Idaho taxable income. Filing status primarily impacts the deduction amount, not the rate.
What income should I enter?
Enter your annual gross wages before taxes. If you want a per‑paycheck estimate, toggle Per‑Paycheck mode and choose your pay frequency.
Does this include federal withholding and FICA?
No. This calculator focuses on Idaho state income tax only. It does not include federal income tax, Social Security, or Medicare.
How accurate is the standard deduction?
The tool uses federal 2024 standard deduction values by filing status, which Idaho generally follows for taxable income. Complex adjustments outside scope may apply to your situation.
Can I include the Idaho grocery tax credit?
You can enter any known Idaho credit in the Credits field. Because eligibility and amounts vary, consult the Idaho State Tax Commission or a tax professional for your exact value.
Why does my effective rate look lower than 5.8%?
Effective rate is relative to gross income. Pre‑tax contributions and deductions reduce taxable income, so the effective rate on gross may be below 5.8%.
Will you update for future tax years?
Yes. We monitor official sources and update rates and thresholds when authorities publish changes.