📐 Math & Everyday calculators
Everyday arithmetic. Percentages in every shape they come in, an age worked out to the second, and two calculators: a plain one for the sums you do in your head, and a scientific one with brackets, powers and angles.
Percentage Calculator
Every shape a percentage question comes in — a percent of a number, one number as a percent of another, increases, discounts, working back to the whole, percentage points — each on a line of its own with the workings underneath.
Open calculator →Age Calculator
How old, down to the second. Put in a date of birth and a date to count to — today, if you like — and see the age in years, months and days, then in days, hours, minutes and seconds with the seconds running.
Open calculator →Calculator
The everyday pad. The sum stays on the screen as it is typed, the running answer sits under it, and times and divide are worked out in the right order rather than behind your back.
Open calculator →Scientific Calculator
Brackets, powers and roots, logarithms, trigonometry, factorials and a memory — with degrees or radians said out loud on the display, since that one setting changes what an answer means.
Open calculator →Figures worth a second look
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Does a 20% fall need a 20% rise to undo it?
No. $50,000 cut by 20% is $40,000, and getting back to $50,000 takes a 25% rise. The two percentages are measured from different starting points, which is why they differ.
Work it out: Percentage → -
When do you turn 10,000 days old?
The 10,000th day of life falls at about 27 years and four months — a birthday nobody sends a card for. The 20,000th arrives at about 54 years and nine months.
Work it out: Age → -
What does 1% a day come to?
1.01 to the power of 365 is about 37.8 — a 1% improvement a day, compounded for a year. The same slide the other way, 0.99 to the same power, leaves about 0.0255.
Work it out: Scientific calculator → -
Why does 0.1 + 0.2 come out as 0.3?
The display rounds: in raw floating point the answer is 0.30000000000000004. A calculator keeps fifteen significant digits and rounds the last one away, which is why this one and the calculator on your phone both show 0.3.
Work it out: Calculator →
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