Financial calculators that show their formula
Free calculators for saving, interest, budgeting, investing and credit – with a transparent calculation path, tested examples and clearly stated limits. No product recommendations, no account, no data collection.
- Open formula: every calculator explains how it computes – with variables and examples.
- In your browser: your inputs are neither stored nor transmitted.
- Neutral: no product recommendations, no “current rates”, no advice.
- Tested: every calculation function passes automated tests with edge cases.
Calculators
- Saving & interest
Compound interest calculator
See how a starting amount and monthly contributions grow with compound interest, with an open formula, a year-by-year table and worked examples in your browser.
- Saving & interest
Savings goal calculator
Work out any of five figures for a savings plan: the final balance, the monthly amount to reach a goal, how long it takes, the starting sum or the rate needed.
- Saving & interest
Inflation calculator
See how inflation erodes money both ways: what a sum today is worth later, and what a future sum is worth in today's money — loss shown in your currency and per cent.
- Budget & reserves
Emergency fund calculator
Work out how big your emergency fund should be and when you'll have it: set your own months of cover and see the target, the gap, progress and time to reach it.
- Budget & reserves
Household budget calculator
Plan a monthly budget: enter income and expenses to see the balance, your savings rate and how spending splits — with an optional 50/30/20 check, in your browser.
- Budget & reserves
Savings rate calculator
Work out your savings rate from income and what you save — or the amount a target rate needs — and see the long-run effect of saving one point more.
- Saving & interest
Savings interest calculator
See the interest and final balance a savings deposit earns at a rate you choose — easy-access or fixed-term, with a compounding schedule and effective annual rate.
- Investing & returns
Fund fees calculator
See how an ongoing charge and other fund fees quietly eat into an investment over the years — your own assumptions, no product data, all in your browser.
- Investing & returns
CAGR calculator
Work out total return, the annualised return (CAGR) or a target value from a start and end value — no interim cash flows, neutral and in your browser.
- Saving & interest
Real return calculator
Work out your real return after inflation and fees with the exact Fisher relationship — and see how far the 'nominal minus inflation' rule of thumb is off.
- Investing & returns
Dividend calculator
Work out a dividend yield, project payouts at an assumed growth rate and see how reinvestment compounds shares — with yield on cost, neutral and in your browser.
- Investing & returns
Lump sum vs phased investing calculator
Compare, neutrally, what investing a sum all at once or spreading it over months gives at your assumed return — no recommendation, all in your browser.
- Investing & returns
Average cost calculator
Work out the weighted average price you paid across several purchases, with and without fees, plus an optional unrealised gain or loss — neutral, in your browser.
- Cars & mobility
Fuel cost calculator
Work out fuel or electricity cost per trip, month and year — with your own consumption and price, cost sharing, commute mode and a scenario comparison.
- Property & housing
German property purchase costs calculator
Estimate the extra costs of buying property in Germany — land transfer tax, notary, land registry and estate agent — with your own rates, in EUR, in your browser.
- Cars & mobility
Car running costs calculator
Work out a car's real running costs — depreciation, insurance, tax, servicing, repairs, tyres and energy — per month and per km, with an A/B comparison.
- Property & housing
Rent vs buy calculator (Germany)
Buy, or rent and invest the difference? A neutral wealth comparison of both paths for the German market — year by year on your assumptions, no recommendation.
- Credit & repayment
Loan refinancing calculator
See whether refinancing a loan pays off: total cost of the old and the new loan, the saving after switching costs and the break-even point — neutral, no providers.
- Everyday & work
Hourly wage calculator
Convert a gross monthly or annual salary to an hourly rate — and back (52 weeks/year) — plus how many working hours a purchase costs. Gross only, no tax.
- Credit & repayment
Overdraft interest calculator
Work out the daily interest an overdraft costs — for a period, per month and per year (actual/365) — plus a comparison with a rate you choose, in your browser.
- Credit & repayment
Effective interest rate calculator
Find a loan's effective annual rate from its payments and fees as the internal rate of return, or convert a nominal rate to the effective one — in your browser.
- Cars & mobility
Lease vs buy calculator
Compare the total cost of leasing and buying a car over the same period — deposit, payments, fees, excess mileage, financing and resale value. Neutral, not advice.
- Budget & reserves
Subscription & fixed-cost calculator
Convert subscriptions and fixed costs at any payment interval to monthly and yearly totals — with the largest cost driver and an optional invest-instead scenario.
Browse all calculators – the portal grows step by step with further tested calculators.
Why you can trust the results
Every calculator is based on an independently tested calculation function: at least five automated tests, edge-case tests and control calculations against independently derived reference values. Assumptions and limits are shown visibly on every calculator page – and where numbers are examples, they are explicitly marked as an example assumption. Your inputs stay in your browser, without an account and without tracking.