Free online calculators
Calculators that show their working, so you can check them.
Paycheck is finished and checked. The rest are being built, one at a time, to the same standard.
Take-home pay for all 50 states and DC, hourly and salary, bonuses.
Open the calculator →Income tax by state, withholding, bonuses, self-employment.
in buildAmortisation, VA and FHA limits, refinancing, student loans.
in buildMargin, commission, equity dilution, cost of capital, pricing.
in buildProbability, distributions, percentages, conversions.
in buildWhile you are here
The machine this site is named after has a genuinely good story. Open whichever bit interests you.
In 1967 a handheld calculator was a laboratory prototype at Texas Instruments. By 1972 you could buy one that did trigonometry. The hinge was 1971, when the logic that had needed hundreds of transistors was squeezed onto a single chip, and the price fell from hundreds of dollars to a few.
PEMDAS and BODMAS are the same rule with different names. The fight is over one thing neither of them settles: whether multiplication written without a sign, like 2(2 + 2), binds tighter than division. Calculators disagree too, and so do Excel and Google.
For about 350 years engineers multiplied by adding lengths on a logarithmic scale. Pickett slide rules flew on the Apollo missions. Then the HP-35 arrived in 1972 and production stopped within a few years.
In Tokyo in November 1946, a champion soroban operator from Japan’s postal savings bureau took on a US Army private working an electric calculator. The abacus won four events to one.
Turn a calculator upside down and the digits become letters. It has been a playground joke since the 1970s, and it even made it onto an album title.
Power, a keypad, a display and a chip. Most calculators count in decimal rather than binary, which is slower but is why they tell you 0.1 + 0.2 = 0.3 when a carelessly written program does not.
Basic, scientific, graphing, programmable, specialised, and software, which is this site. No hardware limit means a tool can be as specific as the job needs.