Every everyday calculator. Instant, free, private.
Live answers as you type — with the formula shown, on every page. Nothing you enter leaves your browser.
Finance →
Loans, interest, VAT — the money math, done right.
Loan repayment Monthly payment, total interest, year-by-year table Bond repayment (South Africa) Home price, deposit, prime-linked rate Compound interest Growth with monthly deposits 401(k) calculator Retirement balance with employer match Personal loan Monthly payment and total interest Car loan Payment with down payment and trade-in Student loan Monthly payment and total interest on a study loan Loan affordability The biggest loan a monthly budget supports Loan payoff (extra payments) Time and interest saved by paying extra Credit card payoff Months and interest to clear a card balance Refinance Monthly saving and break-even on a refinance Down payment Deposit amount and the loan it leaves Balloon payment Lower monthly with a lump sum due at the end HELOC Interest-only payment on a line of credit APR calculator Effective APR once fees are included Roth IRA Tax-free retirement growth with contributions Retirement Nest egg and the income it provides FIRE calculator Your financial-independence number and timeline ROI calculator Return, profit and annualised rate Dividend / DRIP Reinvested dividends compounded over time Net worth Assets minus liabilities, at a glance Inflation What money will be worth in the future CD / fixed deposit Maturity value of a fixed-term deposit Annuity income Monthly income a lump sum can pay out Rule of 72 Years for money to double at a given rate SIP calculator Systematic monthly investing outcome Personal loan (South Africa) Rand repayment with NCA-capped rates Car finance (South Africa) Rand vehicle finance with deposit Amortization schedule Year-by-year interest, principal and balance Debt snowball Payoff timeline, smallest balance first Debt avalanche Cheapest payoff, highest rate first Simple interest I = P×r×t, with the compound comparison Savings goal Months (and the date) until your target VAT calculator Add or remove VAT — 15% ZA or any rate Tip calculator Tip, total, and the per-person split Discount calculator Sale price, savings, stacked discounts Mortgage calculator (UK) Price, deposit, rate — repayment + LTV Mortgage calculator (US) P&I plus taxes and insurance, 30/15-year Salary to hourly Rate, weekly, monthly + overtime 1.5× Fuel cost Trip cost from distance, L/100km, price
Health →
The standard formulas, cited — with their limits stated.
BMI calculator kg/cm or lbs/ft, WHO categories Calorie calculator (TDEE) Maintenance, cut, and gain targets BMR calculator Calories burned at complete rest Ideal weight Devine formula + the healthy range Body fat (Navy) Tape-measure estimate, honest ±3% Water intake Daily target from weight and training Due date Naegele’s rule, week and trimester Pace calculator Min/km, min/mile + race projections One rep max Epley & Brzycki + training percentages Macro calculator Protein, carbs, fat from your calories Ovulation Fertile window from your last period
Dates →
Ages, gaps, and countdowns on the real calendar.
Age calculator Exact years, months, days — and total days Days between dates Exact count, weeks, weekday estimate Add or subtract days What date is 90 days from today Countdown Live days, hours, minutes to any date Hours worked Shift length with breaks, decimal + h:mm Sleep cycles Bedtimes that dodge mid-cycle alarms Days until… Live countdowns: Christmas, Easter, New Year +8 more Dog age Real human years — 2019 formula, not ×7
Math →
The everyday math questions, answered live.
Percentage calculator % of, what %, and % change Average calculator Mean, median, min/max of any list Ratio calculator Simplify and scale — 1920:1080 → 16:9 Fraction ↔ decimal Both directions, with the chart Rule of three A:B = C:X — proportions solved Weighted average Grades and scores: Σ(v×w) ÷ Σw, live Grade calculator Current grade + what you need on the final GPA calculator 4.0 scale × credit hours, live Standard deviation Sample & population, with steps Square footage Feet & inches in, sq ft + m² out
Converters →
Exact unit conversions with reference charts.
CM to inches Exact ÷2.54, with feet & inches KG to lbs Exact definition, not the 2.2 shortcut Meters to feet Rooms, pools, and altitudes KM to miles With the 5K/marathon chart °C to °F Fevers, weather, and oven marks ML to cups The baking chart, US cup honest KM/H to MPH Speed limits and treadmill paces MB to GB Decimal vs binary, told honestly Inches to CM Exact ×2.54 — screens, sewing, DIY Lbs to KG Bodyweight and luggage, exact definition Feet to meters Ceilings to altitudes, exact ×0.3048 Miles to KM Races and road trips, exact ×1.609 °F to °C Fevers and ovens — (°F−32)×5⁄9 Cups to ML US recipes in metric, fractions included MPH to KM/H US limits and treadmills, exact GB to MB Plans and drives — the ×1,000 direction Oz to grams Weight oz for recipes — exact 28.3495 Grams to oz Metric recipes into US kitchens ML to oz US fluid ounces — cans and carry-ons Oz to ML Cocktails and bottles — ×29.5735 Stone to KG UK body weight into metric, exact KG to stone With the stones-and-pounds split Liters to gallons US gallons — fuel and tanks Gallons to liters Exact ×3.785411784, mpg caveats MM to inches Workshop sizes with fraction chart Inches to MM Fractions in, exact metric out CM to feet Heights with the ft-and-inches split Feet to CM Heights and rooms — exact ×30.48 Yards to meters Fabric and fairways — exact ×0.9144 Meters to yards Pools and pitches, exact division
Compliance →
South African statutory deadlines — when filings are actually due.
Why CalcOtter
100 calculators and growing, built on three rules. Instant: results update as you type — no submit buttons, no page reloads, no waiting. Honest: every page shows its formula with a worked example, cites its sources for health math, and tells you the limits of the number it gives you. Private: the math runs in your browser, so amounts, weights, and dates are never sent to a server — load a page once and it even works offline.