Date Calculator

How to use

1. For a gap, set the first Start date and the End date, then click Calculate Difference. The result is a day count marked earlier, later, or same day.
2. For a shift, use the Add / subtract days block. Set its Start date and Days (+/−). A negative number subtracts.
3. Click Calculate New Date. The result shows the new calendar date and the weekday wording for that date.

When it helps

Earlier means the end date is before the start. Later means the end is after the start. Same day means the two dates match. The day count is the size of the gap, so the direction lives in those words rather than in a minus sign.

The signed day count belongs only to Calculate New Date. When the span is really an age, the age calculator breaks a birth date into years, months, and days. A countdown is the live timer when you want time remaining toward a moment, not a fixed day total between two dates.

Limits

All three date fields start as today, and Days (+/−) starts at 30. A blank or non-numeric day count is treated as zero, so Calculate New Date then repeats the start date. Broken dates show Invalid dates on the difference, or Invalid date on the new-date line.

Calculate Difference does not return a negative number. It returns the absolute day count plus earlier, later, or same day. The page does not count business days or holidays, does not list weeks as their own unit, and does not take a clock time.