Find the exact number of days, weeks, months, and years between any two dates.
This calculator finds the exact difference between any two dates in years, months, days, weeks, and total days. It accounts for the irregular structure of the Gregorian calendar, where months have 28 to 31 days, leap years add February 29, and century years follow special rules. The result shows both the calendar-style breakdown (years, months, days) and absolute totals (total days, total weeks, total hours).
The calculation follows the same logic your brain uses but handles edge cases precisely. Moving from January 31 to February 28 is one month, even though only 28 days passed. Moving from January 31 to March 1 is one month and one day in a non-leap year. These month-boundary calculations are where mental math breaks down and a precise tool becomes useful.
Contract and lease calculations frequently require exact day counts. A 90-day return window, a 180-day escrow period, or a 365-day warranty all need a precise target date. Employment law often hinges on exact tenure: FMLA eligibility requires 12 months and 1,250 hours, and probationary periods are measured in calendar days. Getting these numbers wrong can have legal and financial consequences.
Project managers use date differences for sprint planning, deadline tracking, and milestone calculations. Medical professionals calculate gestational age in weeks and days, medication durations, and follow-up intervals. Astronomers measure time in Julian Day Numbers, a continuous count of days since January 1, 4713 BC, to avoid calendar complications entirely.
Calendar days include every day on the calendar, including weekends and holidays. Business days exclude Saturdays, Sundays, and typically federal holidays. A "10 business day" timeline is usually 14 calendar days, but can stretch to 16 or more if holidays fall within the period. Legal deadlines, SEC filing windows, and shipping estimates may specify one or the other, so the distinction matters.
This calculator provides calendar day counts. For rough business day estimates, multiply calendar days by 5/7. For precise business day calculations that account for specific holidays, dedicated business day calculators are more appropriate. The Countdown Calculator can track days remaining to a specific target date.
Before the Gregorian calendar was adopted (1582 in Catholic countries, 1752 in Britain and its colonies), the Julian calendar was used. The Julian calendar assumed a year was exactly 365.25 days, which overestimates by about 11 minutes per year. By the 16th century, the calendar had drifted 10 days from the astronomical year. The Gregorian reform dropped 10 days and refined the leap year rule to correct this drift. When calculating dates across the Julian-Gregorian transition, be aware that historical dates may refer to either calendar system, which can cause apparent discrepancies of up to 13 days.
Date calculations involve more complexity than simple arithmetic due to the irregular structure of our calendar. Month lengths vary (28, 29, 30, or 31 days), leap years add a day every 4 years (with century exceptions), and time zones can shift dates for events spanning midnight. Business day calculations must exclude weekends and optionally holidays. The Gregorian calendar we use today was adopted in 1582 by Catholic countries but not until 1752 in Britain and its colonies, creating historical date ambiguity. The Julian Day Number system, used in astronomy and computing, assigns a sequential day number to every date, eliminating the complexity of calendar date math. For practical purposes: a year has approximately 365.25 days, 52.18 weeks, or 8,766 hours.