Calendar math without hidden assumptions

Dates are easier when the rules are plain.

Calculate date differences, move a date forward or backward, and work with business days. Every result explains which dates were counted.

Calendar dateLocal tool

Built for the awkward dates too: month ends, leap years, and reversed ranges.

10 focused tools

Choose the calculation you need

No sign-up, no date uploads, and no guessing whether an end date was included.

Compare two calendar dates with a consistent end-date rule.

Move a date by days, weeks, months, or years.

Count or add weekdays with optional custom holidays.

Count full calendar days to a date and download an all-day calendar event.

Calculate age, birth weekday, and the next birthday.

Find the weekday, day of year, and ISO week for a date.

Convert dates to ISO weeks or look up a week’s date range.

Add or subtract hours and minutes with day-offset reporting.

Convert seconds or milliseconds to UTC and local time.

Generate a clean monthly calendar with either week-start convention.

How Plain Dates works

Dates are treated as calendar dates rather than time-zone moments, preventing daylight-saving transitions from changing a day count.

Tools say whether the final date is included and how month-end dates or weekends are handled.

Calculations happen in your browser. The dates entered into these tools are not sent to us or stored.