Date Duration Calculator

The date duration calculator does two things. It counts the number of days, weeks, months, and years between two dates (including business days vs weekend days). And it adds or subtracts any combination of years, months, weeks, and days from a starting date to find a future or past date. All of it runs in your browser using UTC date math to avoid daylight-saving bugs.

The basic count is the later date minus the earlier date. The subtlety is whether to include the end date:

• Exclusive (default): June 1 to June 8 = 7 days. This is the gap, like counting nights in a hotel.
• Inclusive: June 1 to June 8 = 8 days. This counts both endpoints, like counting days an event runs.

The calculator also breaks the duration into a calendar-aware years/months/days format, so 400 days becomes "1 year, 1 month, 5 days" rather than a raw number.

The calculator separates business days (Monday through Friday) from weekend days (Saturday and Sunday). This is useful for:

Set a starting date, choose add or subtract, and enter any combination of years, months, weeks, and days. Common uses:

• Return windows: 'purchased + 30 days' for a refund deadline
• Contract terms: 'signed + 1 year' for a renewal date
• Visa durations: 'entry + 90 days' for a stay limit
• Project milestones: 'kickoff + 6 weeks' for a checkpoint
• Medical: 'last dose + 14 days' for a follow-up

Month and year math follows calendar rules: adding 1 month to January 31 gives February 28 (or 29 in a leap year), since there's no February 31.

Date-only calculations in local time can break around daylight saving transitions, where a "day" might be 23 or 25 hours. Computing in UTC (where every day is exactly 24 hours) avoids off-by-one errors. Since this tool works with dates, not specific times of day, UTC gives clean, correct results.

How many days are between two dates?

Subtract the earlier from the later. The calculator does this and also shows weeks, an average month count, years, and a precise years/months/days breakdown.

How do I count days until a future event?

Set today as the start and the event as the end date. The total days is your countdown. Popular for weddings, exams, vacations, and product launches.

What's the difference between calendar days and business days?

Calendar days count every day. Business days count only Monday through Friday. A 10-business-day period spans 14 calendar days (two weekends). Always confirm which a contract or service means.

How do I add 90 days to a date?

Use the add/subtract tab, set days to 90, choose 'Add'. The tool returns the exact date and day of the week. Common for return windows and visa stays.

Does the calculator handle leap years?

Yes. Leap years (Feb 29) are handled automatically in both the day count and the add/subtract math. Adding a year to Feb 29, 2024 gives Feb 28, 2025, since 2025 isn't a leap year.

Why might my count be off by one?

Almost always the inclusive vs exclusive end date. Toggle the 'include the end date' checkbox to switch between counting the gap (exclusive) and counting both endpoints (inclusive).

A quick reference for how many days common time periods work out to. Use it to sanity-check a days between dates calculation or to convert weeks and months into a day count.

Month lengths vary from 28 to 31 days, so any figure tied to months is an average. For an exact count between two specific dates, enter them above and read the calendar-aware total.

There are two correct ways to count, and picking the right one is what usually causes an off-by-one difference. Exclusive counting measures the gap between the dates, while inclusive counting counts both the start day and the end day.

• Exclusive count (the gap): later date minus earlier date. This is the default and matches how you count nights in a hotel.
• Inclusive count (both endpoints): the gap plus 1. This matches how you count the days an event or trip runs.

Worked example from March 1 to March 10: 10 - 1 = 9 days for the exclusive gap, and 9 + 1 = 10 days when you include both the start and end date. Same two dates, two valid answers, so always confirm which count a form or contract expects.

A date to date duration calculator can total every day on the calendar or only the working days. Calendar days count all seven days of the week. Business days count Monday through Friday and exclude weekends, and true working-day counts also exclude public holidays.

• Calendar days: every day between the two dates, weekends included.
• Business days: weekdays only, so a 7 calendar day span is usually 5 business days.
• Holidays: national and regional holidays that fall on a weekday reduce the business-day total further and vary by country.

How many days are between two dates?

Enter the earlier date as the start and the later date as the end, and this how many days between calculator subtracts one from the other. It shows the total days plus weeks, an average month count, years, and a precise years, months, and days breakdown.

How do I calculate the number of days between dates?

By hand, subtract the earlier date from the later date, adjusting for month lengths and any leap year in the range. That is easy to get wrong across month and year boundaries, so this calculator between two dates does the arithmetic for you and returns an exact day count instantly in your browser.

How many days between 2 dates, and does the count include both the start and end date?

By default the count is exclusive, so it measures the gap and does not add the final day. To include both the start and the end date, switch to the inclusive count, which adds 1 to the total. That single toggle explains most off-by-one differences between two calculators.

Is this the same as a date to date calculator?

Yes. A days between dates calculator, a date to date duration calculator, and a calculator between two dates all describe the same task: measuring the span from one calendar date to another. Enter both dates above to get the answer in days, weeks, months, and years.