Dates and age, percentages, discounts, tips and conversions.
Everyday arithmetic keeps coming up: sale prices, tips, elapsed days, time intervals. This guide covers the calculations people reach for most often and the tool for each.
Counting days between dates trips people up because months are not the same length and February occasionally has 29. The Age Calculator gives an exact age in years, months and days, and works for any past or future date. For time within a single day, the Time Duration Calculator returns hours and minutes between two clock times, including overnight shifts.
Percentages show up in tips, taxes, discounts and growth rates. The most common mistake is adding two discounts together. Stacked discounts are applied sequentially, not summed: 20% off then 10% off is a 28% total reduction, not 30%. The Discount Calculator handles the math, and the Tip Calculator covers restaurant tips with optional bill splitting.
Some conversions come up more than expected. Turning a year into Roman numerals for a title, a tattoo, or a cornerstone is a real need, it turns out, and not a trivial one. The Roman Numeral Converter handles 1 through 3,999, the standard range. Roman numerals have no zero and use subtractive pairs like IV (4) and IX (9).
Every calculator here runs entirely in your browser. Nothing you type is sent to a server or stored. That means they are fast, private, and usable offline once the page loads. They are built for practical questions that come up during a normal day, not for enterprise reporting.
The main thing to watch is units and order of operations. Enter times in the right format, apply discounts one at a time, and remember that 'percent of' and 'percent change' are different calculations. When in doubt, sanity-check the result: 25% off $80 should be close to $60. If it is not, re-check the inputs.
Use the Age Calculator. It returns exact years, months and days, with leap years included.
Apply them one at a time. Adding the percentages together gives the wrong answer.
15 to 20 percent of the pre-tax bill for table service in the US.
1 through 3,999. There is no Roman numeral for zero.
No. Every calculator runs in your browser.