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Head-to-head · Tax Calculators

IRS Tax Withholding Estimator vs GOV.UK Self Assessment Tax Calculator

  • Updated Oct 2026
  • Both researched from official sources
  • 1 check side by side
Higher score IRS Tax Withholding Estimator #4 in Tax Calculators 8.6/10 Free plan Free plan Visit IRS Estimator
GOV.UK Self Assessment Tax Calculator #5 in Tax Calculators 8.5/10 Free plan Free plan Visit GOV.UK

IRS Tax Withholding Estimator leads on 0 checks, GOV.UK Self Assessment Tax Calculator on 0, and 1 is even. Who comes out ahead on the 1 yes/no, price and count check where we have data for both products. The editor score weighs everything else too.

Our verdict

  • Highest scoreIRS Tax Withholding Estimator · 8.6/10
  • Free planboth

IRS Tax Withholding Estimator scores higher on our rubric for tax calculators: 8.6 against 8.5 out of 10; our editors rank them #4 and #5.

IRS Tax Withholding Estimator is the better fit for U.S. workers adjusting federal withholding. GOV.UK Self Assessment Tax Calculator is the better fit for UK self-employed people with mixed income.

  • IRS Tax Withholding Estimator fits best

    U.S. workers adjusting federal withholding

  • GOV.UK Self Assessment Tax Calculator fits best

    UK self-employed people with mixed income

Advertiser disclosure: iTechGuides is reader-supported. Vendors can pay for top positions in our rankings and for a place on other products' pages, and we may earn a commission when you click some links. How we rank.

Side by side

Feature IRS Tax Withholding Estimator 8.6/10 Visit ↗ GOV.UK Self Assessment Tax Calculator 8.5/10 Visit ↗
At a glance
Editor score 8.6 8.5
Ranking #4 in Tax Calculators #5 in Tax Calculators
Best for U.S. workers adjusting federal withholding UK self-employed people with mixed income
Pricing model Free Free
Starting price Free plan Free plan
Free plan ✓ ✓
Free trial — —
Deployment Cloud Cloud
Platforms Web Web
Support Docs Docs
Built for Solo Solo
Specs
Calculator types Federal income tax withholding estimator; refund or tax owed estimate Income Tax; Class 4 National Insurance
Tax jurisdictions Federal Federal
Income sources Wages; pension; annuity; self-employment or gig work; Social Security; other income self-employment profits; property rental income; State or occupational pension; paid employment
Filing statuses Not checked yet Not checked yet
Tax years Not checked yet 2025 to 2026
Platforms web web
Our review
Pros
  • Estimates withholding across wages, pensions, and annuities
  • Accounts for income, adjustments, deductions, and credits
  • Downloads completed Form W-4 or W-4P
  • Estimates Income Tax for the 2025 to 2026 tax year
  • Includes Class 4 National Insurance for self-employed users
  • Combines self-employment, rental, pension, and employment income
Cons
  • Covers federal withholding, not state taxes
  • Does not recommend withholding for Social Security or unemployment insurance
  • Does not support nonresident filers
  • Assumes the standard Personal Allowance
  • Does not account for savings and investment income
  • Excludes the High Income Child Benefit Charge and amounts already paid
Our verdict

For workers with wages, a pension, or an annuity subject to federal income tax withholding, the IRS Tax Withholding Estimator offers a free way to check whether withholding is appropriate. It considers income, adjustments, deductions, and…

Read the review →

GOV.UK’s Self Assessment Tax Calculator is a free web tool from HM Revenue & Customs for estimating Income Tax for the 2025 to 2026 tax year. For self-employed users, it also estimates Class 4 National Insurance. It is aimed at people who…

Read the review →
  1. IRS Tax Withholding EstimatorTax Calculators 8.6Free plan
  2. GOV.UK Self Assessment Tax CalculatorTax Calculators 8.5Free plan

Strengths and trade-offs

  • IRS Tax Withholding Estimator — where it wins

    • Estimates withholding across wages, pensions, and annuities
    • Accounts for income, adjustments, deductions, and credits
    • Downloads completed Form W-4 or W-4P

    Where it doesn't

    • Covers federal withholding, not state taxes
    • Does not recommend withholding for Social Security or unemployment insurance
    • Does not support nonresident filers

  • GOV.UK Self Assessment Tax Calculator — where it wins

    • Estimates Income Tax for the 2025 to 2026 tax year
    • Includes Class 4 National Insurance for self-employed users
    • Combines self-employment, rental, pension, and employment income

    Where it doesn't

    • Assumes the standard Personal Allowance
    • Does not account for savings and investment income
    • Excludes the High Income Child Benefit Charge and amounts already paid
  • IRS Tax Withholding Estimator8.6/10 · Free plan

    A free federal estimator that recommends withholding adjustments and prepares W-4 forms.

    Visit IRS EstimatorFull verdict →
  • GOV.UK Self Assessment Tax Calculator8.5/10 · Free plan

    A free web calculator for estimating 2025–26 tax across several income sources.

    Visit GOV.UKFull verdict →

More comparisons

All tax calculators comparisons → · Full ranking →

Guides on tax calculators

Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026

Last updated · How we research and update