Calculate the exact time between any two dates in all units simultaneously: years, months, weeks, days, hours, minutes, and seconds. Includes business days, date+time precision mode, live countdown for future dates, inclusive/exclusive end date, swap dates, copy, and share — features no single competitor offers combined.
What is the time between two dates?
The time between two dates is the exact duration separating two calendar points, measured by the ISO 8601:2019 interval arithmetic standard. Duration breaks into two forms: calendar duration (years, months, and days using exact month lengths) and total duration (a single unit — total days, hours, or seconds). Both are shown simultaneously above. Most calculators show only one; this tool shows all eight.
How do you calculate the number of days between two dates?
Days between two dates equals the end date's Julian Day Number minus the start date's Julian Day Number. The Julian Day Number converts any Gregorian calendar date to a continuous integer count, eliminating the need to track month lengths or leap years manually. For dates within the same month, subtract the day numbers directly: April 14 to April 28 = 14 days.
For dates spanning multiple months or years, the standard algorithm proceeds as follows. Convert both dates to a total day count from a fixed epoch (January 1 of a reference year). Subtract the smaller from the larger. Add one if the inclusive end date option is selected. The result is precise to the calendar day regardless of month length variation (28, 29, 30, or 31 days per month) and leap year occurrence.
To calculate the time between dates manually, follow these steps. First, count complete years between the dates. Second, count remaining complete months after those full years. Third, count remaining days after those full months. Concatenate the three values as years/months/days for the calendar duration. For total days, multiply years by 365.25 (average) or compute from exact epoch counts for precision.
What is the difference between calendar duration and total days?
Calendar duration expresses elapsed time as years, months, and days — for example, "2 years, 3 months, 14 days." It uses exact Gregorian month lengths and accounts for leap years. Total days expresses the same interval as a single integer — for example, "848 days" — useful for deadline calculations, age in days, and project management.
The distinction matters because one calendar month is not always 30 days. January has 31 days; February has 28 or 29; April has 30. "3 months" starting January 1 ends April 1 (90 days); "3 months" starting March 1 ends June 1 (92 days). Total days is always unambiguous. Calendar duration is more human-readable. This calculator displays both simultaneously — no unit switching required, unlike all nine competitors listed on this page.
For chronological age calculations specifically — measuring exact age from a date of birth — the Age Calculator applies the same ISO 8601 interval arithmetic and additionally outputs the next birthday countdown, zodiac sign, and generation label.
How are business days between two dates calculated?
Business days (working days) between two dates equal the total calendar days minus weekend days (Saturdays and Sundays). The formula uses full weeks to achieve O(1) performance: business_days = floor(total_days / 7) × 5, plus the count of weekdays in the remaining days. A remaining-days loop runs at most 6 iterations, checking the day-of-week (ISO weekday: 1 = Monday, 7 = Sunday) for each day.
Business day calculation applies directly to employment law (notice periods, statutory deadlines), project management (sprint duration, delivery SLAs), and financial contracts (settlement dates, invoice payment terms). Public holiday exclusion varies by country and jurisdiction; this calculator excludes Saturdays and Sundays universally and displays both total days and business days side by side for direct comparison.
For employment duration specifically — calculating years of service, pension eligibility, or notice period entitlement — use the Years of Service Calculator, which outputs both calendar duration and business days with explicit month-boundary handling.
What does inclusive vs exclusive end date mean?
Exclusive end date (the default) counts days up to but not including the end date. April 1 to April 5 exclusive = 4 days. Inclusive end date counts the end date itself. April 1 to April 5 inclusive = 5 days. The difference is one day, but the correct choice depends entirely on the use case.
| Use Case | Correct Setting | Reason |
|---|---|---|
| Age calculation (how old am I?) | Exclusive | Age counts up to but not including the reference date — you are not yet the next age on your birthday until midnight passes. |
| Contract duration ("from Jan 1 to Jan 31") | Inclusive | Both Jan 1 and Jan 31 are working days within the contract period — 31 days total. |
| Project sprint (days remaining) | Exclusive | The end date is the deadline; work stops on the preceding day. |
| Ticket/booking duration (3-night stay) | Inclusive | Check-in and check-out dates both count as part of the stay. |
| Legal notice period | Exclusive or Inclusive | Jurisdiction-specific — verify against the applicable statute or contract clause. |
| Age of a document/record | Inclusive | A document dated today is 1 day old at end of the same day, not 0. |
How many days, weeks, and months are in a year?
One Gregorian calendar year contains 365 days in a common year and 366 days in a leap year. One year contains exactly 52 weeks and 1 day (common) or 52 weeks and 2 days (leap). One calendar year contains 12 months. The average year length used in astronomy is 365.2425 days — the Gregorian correction over the Julian calendar's 365.25-day average.
| Unit | Exact Value | Approximate | Notes |
|---|---|---|---|
| Seconds per minute | 60 | 60 | Exact by definition |
| Minutes per hour | 60 | 60 | Exact by definition |
| Hours per day | 24 | 24 | Exact by definition |
| Days per week | 7 | 7 | Exact by definition |
| Days per month | 28–31 | 30.44 | Varies; Feb has 28 or 29 |
| Days per year | 365 or 366 | 365.2425 | Gregorian average |
| Weeks per year | 52 + 1 or 2 days | 52.18 | ISO 8601 week numbering |
| Months per year | 12 | 12 | Exact by definition |
| Seconds per day | 86,400 | 86,400 | Excludes leap seconds |
| Seconds per year | 31,536,000 (common) | 31.56 million | Exact for standard year |
These conversion factors power all unit outputs in the calculator above. When the calculator displays "1,248,300 minutes" between two dates, it multiplies total days by 1,440 (minutes per day). Seconds are computed as total_days × 86,400, with live subtraction for future date countdowns.
What is a leap year and how does it affect date duration?
A leap year is a calendar year containing 366 days, with February 29 as the intercalary (added) day. The Gregorian calendar rule: a year is a leap year if divisible by 4, except century years (divisible by 100) are not leap years unless also divisible by 400. The years 2000 and 2400 are leap years; 1900 and 2100 are not.
Leap years affect date duration calculations in two ways. First, a period spanning a February 29 in a leap year contains one more day than the same nominal period in a non-leap year. February 1 to March 1 is 28 days in a common year and 29 days in a leap year. Second, individuals born on February 29 age legally on February 28 in non-leap years in most jurisdictions, preventing chronological drift. This calculator handles both edge cases automatically. To calculate your precise age accounting for February 29 birth dates, use the Age Calculator.
How do you calculate time between dates including hours and minutes?
To include time precision, switch to "Date + Time Precision" mode in the calculator above. Enter a start date and time (HH:MM) and an end date and time (HH:MM). The calculator converts both to Unix timestamps (seconds elapsed since January 1, 1970, 00:00:00 UTC), subtracts start from end, and decomposes the result into days, hours, minutes, and seconds.
Time precision matters in these scenarios: calculating exact project duration from meeting start to end, determining elapsed time between flight departure and arrival across time zones, measuring interval between clinical events in medical records, and computing overtime pay periods that cross midnight. For a dedicated time-only calculator (without date input), see the Date + Time mode within this tool — no separate tool needed.
The Date + Time mode shares the same new-window print function as the date-only mode — click "Download PDF" to get a clean one-page report with all units, the exact start and end timestamps, and the AgeCalculator.su branding header.
How long ago was a historical date? Common examples answered
Historical duration questions are answered instantly using the presets above — click any event name and today's date is auto-set as the end date. Common examples calculated as of April 2026:
The Apollo 11 moon landing (July 20, 1969) was 56 years, 8 months, and 25 days ago — approximately 20,724 days, 2,960 weeks, or 497,376 hours. The September 11 attacks (September 11, 2001) were 24 years, 7 months, and 3 days ago. The invention of the World Wide Web (August 6, 1991) was 34 years, 8 months, and 8 days ago. The Berlin Wall fell (November 9, 1989) 36 years, 5 months, and 5 days ago.
For questions about how old a person, organisation, or document was on a specific historical date — rather than from a historical date to today — the Age Calculator accepts any reference date, not just today. Enter a historical start date and a historical end date to compute duration between any two points in history.
What is the difference between time since and time until?
Time since measures elapsed duration from a past date to a reference date (usually today). Time until measures remaining duration from a reference date to a future date. Both use identical arithmetic — subtract the earlier date from the later date. The direction of the label changes, not the calculation.
This calculator handles both automatically: past dates produce a "time since" result; future dates produce a "time until" result and additionally activate the live countdown ticker, which counts down in real time — days, hours, minutes, and seconds — updating every second without page reload. Switch to "Countdown" mode to isolate this view. The live ticker uses requestAnimationFrame for smooth updates and zero CPU overhead when the tab is hidden.
Common time until use cases: days until a contract expiry date, weeks until a project deadline, months until a retirement date, or seconds until a scheduled event. The Age Calculator's next birthday countdown uses the same mechanism for a person's upcoming birthday.
Frequently Asked Questions about Time Between Dates
How many days are between two dates?
Days between two dates equal the end date minus the start date in calendar days. April 1 to May 1 = 30 days (exclusive), or 31 days (inclusive). The calculator above computes this instantly and simultaneously displays total weeks, hours, minutes, and seconds without requiring unit selection.
How do I calculate weeks between two dates?
Divide total days by 7. Floor the result to get complete weeks; the remainder is extra days. April 1, 2024 to October 1, 2024 = 183 days = 26 weeks and 1 day. The calculator displays this as "26 weeks + 1 day" in the unit grid — no manual division needed.
What is the fastest way to find the number of months between two dates?
Months = (end year − start year) × 12 + (end month − start month). Adjust by −1 if the end day is less than the start day. January 15 to November 3 = (0 × 12) + (11 − 1) − 1 = 9 months. The calculator also shows this as total approximate months (year × 12 + months) for long-range calculations.
How many hours are between two dates?
Hours = total days × 24. April 1 to May 1 (30 days) = 720 hours. The calculator displays the exact total hours in the unit grid. For hour precision within the same day or across midnight boundaries, use Date + Time Precision mode and enter the exact start and end times.
How many seconds are in a day, week, month, and year?
One day = 86,400 seconds. One week = 604,800 seconds. One average month ≈ 2,629,800 seconds (30.44 days). One common year = 31,536,000 seconds; one leap year = 31,622,400 seconds. The calculator multiplies total calendar days by 86,400 for the total seconds output.
Does February count as 28 or 29 days in the calculation?
February counts as 29 days in any leap year (divisible by 4, except century years not divisible by 400) and 28 days in common years. The calculator uses exact Gregorian calendar month lengths, not fixed 30-day approximations, so all outputs are accurate regardless of which months the date range crosses.
How are business days different from calendar days?
Business days (working days) exclude Saturdays and Sundays. Two weeks (14 calendar days) contain 10 business days. The calculator displays both simultaneously: total calendar days in the primary result and business days in the breakdown panel. Public holidays are not automatically excluded as these vary by country and jurisdiction.
Can this calculator count days from a date in the past to today?
Yes. Enter any past date as the start date and click the "Today" shortcut next to the end date field. The result immediately shows how many years, months, days, hours, minutes, and seconds have elapsed since that date. Historical preset events (Apollo 11, September 11, etc.) auto-populate the start date with a single click.