maratoolFinance calculators
Mortgage, loan, interest, and investment calculators — everything runs locally in your browser.
Mortgage Calculator — Monthly Payment & Amortization
Calculate monthly mortgage payments, total interest, and full amortization schedule. Enter loan amount, rate, and term.
Loan Calculator — Monthly Payment & Interest
Calculate monthly loan payments and total interest for personal, auto, or business loans. See full amortization schedule.
Compound Interest Calculator
Calculate compound interest with monthly contributions. See balance growth over time with a year-by-year breakdown.
CAGR Calculator — Compound Annual Growth Rate
Calculate compound annual growth rate between two values over any time period. Instant CAGR percentage.
FIRE Calculator — Financial Independence Retire Early
Calculate years to financial independence using the 4% rule. Enter savings, expenses, income, and savings rate.
Inflation Calculator — Purchasing Power Over Time
See how inflation erodes purchasing power. Enter an amount and year range using historical US CPI data.
Stock Average Price Calculator — Cost Basis
Calculate weighted average share price across multiple purchases. Enter shares and price per lot.
Dollar Cost Averaging Calculator
Model dollar-cost averaging with recurring investments. See average cost per share and total invested.
DCF Calculator — Discounted Cash Flow NPV
Discount a stream of future cash flows back to today at a rate you choose, and see the net present value plus what each year contributes.
Position Size Calculator — Risk per Trade
Work back from the money you are willing to lose and your stop distance to the position size that risks exactly that and no more.
Crypto Profit Calculator
Enter buy price, sell price and position size to see profit, loss and percentage return, with fees taken off both ends of the trade.
Simple Interest Calculator
Calculate simple interest with I = P·r·t. Enter principal, rate, and time in years, months, or days — compare against annual compounding.
Credit Card Interest Calculator
See how long paying off a credit card takes and what it costs. Compare your monthly payment against minimum payments at your APR.
Loan Payoff Calculator
Find your loan payoff date and what extra monthly payments save — months cut and interest saved, side by side with your current plan.
Mortgage Refinance Calculator
Should you refinance? Compare current vs new rate and term: monthly savings, break-even point on closing costs, and lifetime savings.
Debt Payoff Calculator
Plan your debt-free date. List balances, APRs, and minimums, add an extra budget, and compare snowball vs avalanche strategies.
Rent vs Buy Calculator
Compare renting vs buying a home over your time horizon — mortgage, taxes, maintenance, and appreciation against rent growth and investing.
HP 12C Calculator Online
Use the HP 12C financial calculator online: RPN keys, TVM, NPV, IRR, amortization, bonds and programs, with a live stack and paper tape.
About these finance calculators
Personal and business finance decisions often come down to a few numbers — monthly payment, total interest, growth rate, or annual return. These calculators handle the math instantly so you can compare options without opening a spreadsheet.
What you can calculate
Use the mortgage calculator for home loans with full amortization schedules. The loan calculator works for any fixed-rate installment loan in months. The compound interest calculator projects savings growth with optional monthly contributions. The CAGR calculator smooths investment returns to an annual rate.
Privacy
All calculations run in your browser. Loan amounts, rates, and balances never leave your device.