Date Calculator
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How to use
- 1 Choose Days between dates to find the gap between two calendar dates.
- 2 Choose Add / Subtract days to project from a base date forward or backward.
- 3 Pick the dates with the date pickers — defaults to today.
- 4 Click Calculate to see the year/month/day breakdown plus weekday.
- 5 Use cases: project deadlines, return policy windows, contract terms, age in days, pregnancy weeks, anniversary planning.
About Date Calculator
FAQ
Q How many days from today is December 31?
Use the calculator with today as the start and December 31 as the end. The result depends on the current date — for May 7, 2026, December 31 is 238 days away (about 7 months 24 days, or 34 weeks).
Q How many days are between January 1 and December 31?
In a regular year, 364 days exclusive (January 1 + 364 = December 31), or 365 inclusive. In a leap year (2024, 2028, 2032), 365 days exclusive or 366 inclusive. The calculator returns exclusive count by default.
Q Does the calculator count both endpoints?
No — it returns the exclusive day count. June 1 to June 5 returns 4 days. If you need to count both endpoints (typical for renting a hotel for those nights), add 1 to the result.
Q How are leap years handled?
The Gregorian leap-year rule is built in. A year is a leap year if divisible by 4, except if divisible by 100, except if divisible by 400. February 29 dates are counted correctly when both endpoints span a leap year.
Q Can I cross daylight saving time?
Yes. The calculator uses calendar days, not 24-hour blocks, so spring-forward and fall-back transitions do not change the day count between two calendar dates.
Q How accurate is the year/month/day breakdown?
The breakdown uses calendar years and months, not approximations. For example, March 1 to April 30 returns 1 month, 29 days — not "60 days ≈ 2 months." Calendar-based interval math respects month length differences.
Q How do I calculate my IRS tax-filing deadline?
Federal tax day is April 15 (or the next business day if April 15 falls on a weekend or DC holiday). Six-month extensions move the deadline to October 15. Use the calculator to count business days remaining if you're close to a deadline.
Q What is the maximum date range I can use?
The calculator handles dates from year 1 to year 9999 — the full range of PHP DateTime. For practical use, any dates within ±200 years of today work without precision issues.
Official resources
NIST Time and Frequency Division
NIST authoritative US source for calendar and time standards.
ISO 8601 — International Date Format
ISO international standard for date and time representation, including week numbering.
US Naval Observatory: Calendars
US Naval Observatory FAQ on the Gregorian calendar and leap year rules.
Library of Congress — Calendars Through History
Library of Congress reference on the history of the Gregorian calendar adopted in 1582.