Related guides

Solving for the Monthly Payment: The Sinking-Fund Math Behind a Savings Goal

The annuity formula that turns a target amount, a deadline, and an expected return into a single monthly savings number — and why inflation adjusts the target, not the monthly payment directly.

What a Road Trip Actually Costs, Split Per Passenger and Per Kilometer

The arithmetic behind trip fuel cost — distance, consumption, and price per litre — and why per-passenger and per-kilometer cost are the numbers worth comparing against other transport.

The 4% Rule and What It Actually Takes to Retire Early

How the FIRE calculator turns monthly expenses into a savings target using the 4% withdrawal rule, and simulates month by month whether your current contributions get there.

Related tools

Compound Interest Calculator

Project compound growth with an initial amount and monthly contributions — yearly schedule, interest share and chart, all computed in your browser.

Currency Converter

Convert between 30 currencies using an offline rate snapshot with manual rate override — no API calls, works without a network.

Discount & VAT Calculator

Apply discounts and VAT or sales tax in one calculation — supports both VAT-inclusive and VAT-exclusive prices with per-unit and quantity totals.

FIRE & Retirement Calculator

Project a FIRE portfolio target using expenses, savings, contributions and return.

Loan & Mortgage Calculator

Calculate monthly payments, total interest and a full amortization schedule — and see exactly how extra payments shorten your loan.

Savings Goal & Sinking Fund

Calculate monthly sinking-fund contributions with return and inflation assumptions.