About DateMath

DateMath is a free online collection of date and time calculator tools. We provide 20 accurate, easy-to-use calculators covering date arithmetic, age calculation, countdown timers, and calendar reference — everything you need for date and time math in one place.

Why DateMath?

Date calculations are deceptively complex. A simple question like "how many days between January 15 and March 10?" involves accounting for varying month lengths, leap years, and whether to count the start and end dates as inclusive or exclusive. Asking "what is my exact age?" adds the complication of correctly counting years, months, and days without off-by-one errors on birthdays.

DateMath handles all of this complexity automatically using JavaScript's native Date API, which follows the Gregorian calendar specification precisely. Every calculator properly accounts for leap years, month boundaries, and time zone offsets.

Our Calculator Categories

• Date Calculators: Find the number of days, weeks, or months between two dates; add or subtract days from a date; count business days (weekdays only) between dates.
• Age Calculators: Calculate exact age in years, months, and days; find your age in total days, hours, or minutes; calculate what age you were or will be on any specific date.
• Countdown Tools: Live countdowns to Christmas, New Year, and any custom date; count how many days have passed since any past event.
• Date Reference: ISO week number calculator, day-of-year calculator, leap year checker, Unix timestamp converter, and time zone converter.

Technical Accuracy

All DateMath calculations use JavaScript's built-in Date object, which implements the Gregorian calendar and correctly handles:

• Leap years (including the century year exception)
• Varying month lengths (28, 29, 30, and 31 days)
• Year boundaries (e.g., adding 100 days to November correctly rolls into the next year)
• Time zone offsets for countdown timers
• Unix epoch timestamps (milliseconds since January 1, 1970 UTC)

Privacy and Performance

All calculations run entirely in your browser. No dates, inputs, or results are sent to any server. DateMath works offline once loaded, making it reliable in any environment. There is no registration, no subscription, and no usage limits — DateMath is completely free.

Contact

Have questions, found a bug, or want to suggest a new calculator? Visit our contact page to get in touch. We welcome all feedback.