Finance Calculators
Every tool here runs entirely in your browser. No account required, no data sent to a server, no cost.
Compound interest calculator
Sliders, live chart, optional local save of your inputs.
Inflation impact calculator
Purchasing-power decay vs CPI, Rule of 72 context, optional return line and year-by-year chart.
Position sizing calculator (Kelly)
Kelly vs half vs quarter vs fixed-risk sizing: table, KPI row, and comparison chart, private and client-side.
Dollar-cost averaging (DCA) calculator
Modeled pacing vs lump-sum with volatility corridor chart, illustrative assumption-driven math only.
Net worth tracker
Dynamic asset and liability rows, donut and category charts, session-only, never transmitted.
FIRE calculator
FIRE number, years to independence, path chart, and savings-rate sensitivity, localStorage inputs.
Credit card payoff calculator
Minimum vs fixed payments vs payoff-by-date, balance chart and interest totals.
Debt snowball vs avalanche visualizer
Multiple debts, extra budget, months, interest, payoff order, and chart for both strategies.
Mortgage amortization calculator
Amortization table, PMI and escrow, prepayments, CSV export.
Roth vs Traditional IRA comparator
Federal brackets and optional state tax, after-tax projection chart vs Traditional.
Loan payoff strategy calculator
Extra principal each month, months and interest saved vs minimum payment.
Airline Mile Value Calculator
Calculate the real cash value of airline miles and points across major loyalty programs.
What does a finance calculator actually do?
Finance decisions almost always involve more than one variable. Your monthly mortgage payment shifts if you put down 15% instead of 20%. Your retirement balance changes by tens of thousands if you start five years earlier. Your take-home pay looks different in every US state. Ask an AI chat tool how much you will have saved in twenty years and you will get one number, for a hypothetical version of you that shares none of your actual inputs.
A calculator gives you as many answers as you need, and each one is built from your numbers.
Why interactive calculators beat AI for multi-variable finance questions
AI language models return one number for one implicit set of inputs. A browser calculator lets you adjust every variable and see the outcome change in real time.
This gap matters most in finance for three reasons.
Time amplifies small differences. A one-percentage-point difference in annual return over thirty years changes your final balance by more than most people expect. Contributing 00 a month for 30 years at 7% annual return (monthly compounding) produces 43,994. The same inputs at 8% produce 98,072, a 4,078 gap from a single percentage point. That is not a rounding error, it is the price of one wrong assumption.
Personal variables are non-negotiable.Federal tax brackets, state income tax rates, mortgage insurance rules, and contribution limits are all jurisdiction- and situation-specific. An AI answer for “how much will I take home on a 0,000 salary” is correct for exactly one state, one filing status, one 401(k) contribution rate, and one benefits package, none of which the model knows unless you specify all of them. A calculator makes every variable an input field.
Decisions are sequential.Almost every finance question has an immediate follow-up: “OK, if I do that, what happens to this other thing?” That is an iterative process. It requires a tool you can manipulate, not a one-shot response to read and close.
How to pick the right calculator for your question
Use the type of question as your starting point:
- How much will my savings or investments grow? Use the Compound Interest Calculator.
- What will my mortgage cost and how can I pay it off faster? Use the Mortgage Amortization Calculator.
- How much do I actually take home from my salary? Use the Take-Home Pay Calculator (US).
- Should I pay down debt with snowball or avalanche? Use the Debt Snowball vs Avalanche Visualizer.
- How does starting five years earlier change my retirement balance? Use the Compound Interest Calculator.
If your question involves multiple variables, a comparison between two paths, or a timeline spanning years, you want a calculator. A chat tool gives you one answer for one scenario. A calculator gives you the answer for any scenario you care to model.
Why every OnSumo finance tool runs in your browser
Every calculator on this site is client-side. Your income, savings balance, mortgage details, and investment figures never leave your device. No account is required. Nothing is logged or stored.
Financial inputs are sensitive data, salary figures, debt balances, retirement savings, and housing costs are not information most people want stored in a database they do not control. Running the math locally means there is nothing to breach and nothing to track. Close the tab and the data is gone.