Free Online Calculators

How to pick the right calculator

Start from the number you want, not from the category. If you want to know what a house will cost you each month, that is the mortgage calculator; if you want to know how much house you can afford in the first place, that is the house affordability calculator. The two use the same maths in opposite directions, and picking the wrong one is the most common reason a result looks strange.

Every calculator page states its formula and its assumptions in full. Where a result depends on something we cannot know — a tax rate, an interest rate that has not been fixed yet, your actual metabolism — the page says so rather than presenting an estimate as a fact.

Finance calculators

The largest group on the site, at 88 calculators. The mortgage calculator gives a monthly payment with taxes, insurance and PMI; the amortization calculator turns any loan into a payment-by-payment schedule; and the refinance calculator compares a new rate against what you are paying now, including the break-even point on closing costs.

For borrowing there is the loan calculator, auto loan calculator, personal loan calculator and student loan calculator. For saving and investing there is the compound interest calculator, investment calculator, 401k calculator, Roth IRA calculator and retirement calculator. For getting out of debt, the debt payoff calculator and credit card payoff calculator. Tax and pay are covered by the income tax calculator, sales tax calculator and take-home salary calculator.

These are estimates for planning, not advice. Rates, tax rules and lender fees change, and your own numbers will differ from any calculator's defaults.

Health and fitness calculators

36 calculators covering body composition, nutrition and training. The BMI calculator gives your body mass index and the category it falls in; the body fat calculator and lean body mass calculator go further using tape measurements; and the ideal weight calculator shows what the standard formulas suggest for your height.

For food and training there is the calorie calculator, BMR calculator, TDEE calculator, macro calculator, protein calculator and water intake calculator, plus the pace calculator and one rep max calculator for runners and lifters. Pregnancy and cycle tracking are handled by the due date calculator, ovulation calculator and period calculator.

All of these produce population-average estimates from formulas published in the literature. They are not a diagnosis and they are not a substitute for talking to a doctor or a dietitian.

Math calculators

46 calculators for arithmetic through to statistics. The percentage calculator handles the three questions people actually ask — what is X% of Y, X is what percent of Y, and the change from X to Y — while the percentage increase calculator and percentage decrease calculator each own one of those directly.

For everyday maths there is the fraction calculator, ratio calculator, average calculator and rounding calculator. For algebra and number theory, the scientific calculator, exponent calculator, root calculator, GCD calculator, LCM calculator and prime factorization calculator. For statistics, the standard deviation calculator, z-score calculator, confidence interval calculator and p-value calculator. Geometry is covered by the area calculator, volume calculator, triangle calculator and Pythagorean theorem calculator.

Education calculators

The GPA calculator converts letter grades and credit hours into a grade point average on the US 4.0 scale, and the grade calculator works out what you need on a final to reach a target. For Indian universities, the CGPA calculator and SGPA calculator use the 10-point scale instead, and the marks percentage calculator and attendance calculator cover the two things students check most often.

Date and time calculators

The age calculator gives an exact age in years, months and days. The date calculator adds or subtracts a span from a date, the date difference calculator counts the days between two dates, and the business days calculator does the same while skipping weekends.

For hours rather than days, the time duration calculator, hours calculator and time card calculator add up shifts and work out totals for a timesheet.

Business and everyday calculators

The tip calculator splits a bill and works out a tip at any percentage. The discount calculator gives a sale price and the amount saved; the markup calculator and profit margin calculator handle the same relationship from a seller's side; and the break-even calculator shows how many units cover fixed costs.

The everyday group also includes the sleep calculator, the heat index calculator and wind chill calculator, and the subnet calculator for anyone laying out a network.

Construction and trades calculators

20 calculators for people ordering materials. The square footage calculator gives room area in feet, metres or yards; the concrete calculator converts a slab's dimensions into cubic yards and bags; and the tile calculator, roofing calculator, mulch calculator and gravel calculator each work out quantity plus a waste allowance.

On the engineering side, the Ohm's law calculator, voltage drop calculator, resistor calculator and BTU calculator handle electrical and HVAC sizing, and the gas mileage calculator and fuel cost calculator cover running a vehicle.

Calculators and converters are different tools

A calculator applies a formula to your inputs. A converter restates the same quantity in different units. They look similar but the intent is different, so they are kept apart: unit conversions live in the unit converters category, with the most-used pairs — inches to centimetres, kilograms to pounds, Celsius to Fahrenheit — on their own pages with the exact conversion factor written out.

Frequently asked questions