Mortgage, Salary Tax & Retirement Calculators
Precision mathematical models benchmarked against IRS Publication 15-T, HMRC allowances, and CFPB lending rules. Private, fast, and calculated entirely in your browser with zero account requirements.
IRS & HMRC
Statutory brackets
TILA Reg Z
Standard P&I math
0 Trackers
Client-side compute
8 Tools
100% Free access
Verified Model Scenario:
$400,000 Purchase · 20% Down · 6.50% Fixed 30-Year Loan = $2,022.61 / month Principal & Interest
Essential Decision Engines
Explore our core four financial models with live amortization, payroll tax, and retirement compounding telemetry.
Mortgage & Amortisation
Model principal, interest, taxes, insurance, and payoff acceleration with extra monthly payments.
Full schedule & interest curves
Take-Home Pay (US & UK)
Calculate exact net earnings after Federal, State, FICA, UK PAYE, National Insurance, and student loans.
Includes standard deduction & NICs
Retirement & SWR Planner
Forecast portfolio longevity, compound monthly growth, inflation drag, and 4% safe withdrawal amounts.
Real vs nominal purchasing power
Compound Interest & Rule of 72
Visualize how continuous compounding transforms modest monthly contributions over multi-decade horizons.
Rule of 72 doubling timeline
How Our Calculations Are Verified
Every formula in FinanceToolkit is audited against public statutory tables and regulatory documentation. We do not use proprietary opaque estimates:
IRS Publication 15-T
Internal Revenue Service
Federal income tax withholding brackets, standard deductions, and FICA wage caps.
HMRC Rates & Allowances
HM Revenue & Customs
Personal Allowance tapers (£100k+), Class 1 employee NICs, and SDLT residential thresholds.
TILA Reg Z / CFPB Amortisation
Consumer Financial Protection Bureau
Standard monthly principal & interest amortisation formulas and APR calculations.
100% In-Browser Compute
Client-Side Execution
Zero server storage. Salary, loan figures, and balance sheets never leave your machine.
Understand the Underlying Mathematics
Explanatory guides breaking down amortisation mechanics, tax band transitions, and compound return formulas.
15-Year vs 30-Year Mortgage: The Real Math Behind the Payment Gap
A 15-year mortgage saves six figures in interest, but locks you into higher payments. We break down the amortisation trade-off with a $300k loan at 6.50% APR.
Read complete analysisCompound Interest Mechanics: How Regular Contributions Overtake Principal
Why starting earlier beats larger contributions later: the mathematical crossover point where interest exceeds annual deposits, backed by Rule of 72 doubling formulas.
Read complete analysisReady to model your loan, paycheck, or retirement?
Run unlimited calculations locally in your browser. No account registration, zero marketing emails, and 100% private.