About calc.funmagi.com

calc.funmagi.com is a small set of free money calculators made by TanLabs, an independent maker of budget and bookkeeping spreadsheets (our templates on Gumroad). Every calculator answers one everyday question – how long a card takes to pay off, how much rent fits an income, what to charge per hour – and comes with a free spreadsheet that uses the same formulas.

How we check the maths

• Each page shows its formula in plain words under How it's calculated.
• The downloadable .xlsx uses spreadsheet functions (NPER, PMT and plain arithmetic). Before publishing, we recalculate every template in LibreOffice and compare it with the web result for the default inputs.
• Loan and savings maths use monthly compounding (annual rate ÷ 12), which is how most US cards and savings accounts quote rates.
• Rules of thumb (30% rent rule, 50/30/20, 3–6 months of expenses) are labelled as rules of thumb, not personal advice.

What we don't do

We are not a bank, lender or financial adviser and we don't sell your data. Calculations run in your browser; the numbers you type never leave your device.

Contact

Found a mistake or want a calculator added? Email tanlabs@mail.grokbot.com. We fix confirmed errors and note the change date on the page.

All calculators

• Credit Card Payoff Calculator
• Net Worth Calculator
• Profit Margin Calculator
• How Much Rent Can I Afford? Calculator
• Debt Snowball Calculator (vs Avalanche)
• Emergency Fund Calculator
• 50/30/20 Budget Calculator
• Savings Goal Calculator
• Wedding Budget Calculator
• Freelance Hourly Rate Calculator