Add or subtract days, weeks, months, and years, or count business days
Resulting Date
2026-08-14
Friday
Weekday
Friday
ISO Week
33
Day of Year
226
What is a Date Calculator?
A date calculator does two everyday jobs at once. First, it adds or subtracts a span of years, months, weeks, and days to a base date and tells you the exact resulting date — useful for deadlines, contract end dates, warranty expirations, or planning a trip. Second, it counts business days (Monday to Friday) between two dates, which is how shipping estimates, payment terms, and project timelines are usually measured. Doing this by hand is error-prone because months have different lengths and leap years add February 29, so the tool computes everything directly to stay accurate. It also reports the weekday, the ISO 8601 week number, and the day of the year for the result.
How to Use
Add / Subtract mode:
1. Pick a base date.
2. Choose Add or Subtract.
3. Enter any combination of years, months, weeks, and days.
4. Read off the resulting date, its weekday, ISO week, and day of year.
Business Days mode:
1. Enter a start date and an end date.
2. Optionally enter the number of public holidays in the range.
3. See total days, weekdays, weekend days, and the business-day count.
How It Works
Add/Subtract: years and months are applied first, then the day is clamped to the last day of the resulting month, so January 31 + 1 month = February 28/29. Weeks and days are then added as plain day arithmetic. All math is done in UTC to avoid timezone drift.
Business days: every calendar day from start to end (inclusive of both endpoints) is examined; Saturdays and Sundays are counted as weekend days and the rest as weekdays. The business-day total is the weekday count minus any holidays you enter, floored at zero.
Interpreting Results
The resulting date is the calendar date after applying your offsets, with month-end clamping so you never roll into an unexpected month. The ISO week number (1-53) follows the ISO 8601 standard where weeks start on Monday and week 1 contains the year's first Thursday. The day of year (1-366) is handy for scientific and planning use. In business-day mode, remember that the count excludes weekends but only excludes the holidays you supply — this calculator does not know any country's holiday calendar, so add them yourself for an accurate working-day figure.
Frequently Asked Questions
What happens when I add a month to January 31? ▾
The result is February 28 (or February 29 in a leap year). Months are added first and the day is clamped to the end of the target month, so it never spills over into March.
Does the business-day count include weekends? ▾
No. Saturdays and Sundays are excluded from the business-day total. You can also subtract public holidays by entering how many fall on weekdays within the range.
Does the tool know my country's public holidays? ▾
No. It has no built-in holiday database. Enter the number of weekday holidays in the period yourself, and they are subtracted from the business-day total.
Are calculations affected by my timezone? ▾
No. All date math is performed in UTC, so the resulting date and counts are stable regardless of the device's timezone.