Add or subtract days, weeks, months, or years from a date.
Choose your start date, enter a value, set the unit to Days, Weeks, Months, or Years, and select Add. Dayvilo counts forward on the calendar and shows the resulting date and its weekday. For example, August 29, 2026 plus 1 day is August 30, 2026.
Set the operation to Subtract and enter the number of days to count backward. Dayvilo handles month and year boundaries automatically, so March 1, 2028 minus 1 day correctly returns February 29, 2028.
One week always equals seven calendar days. Select the Weeks unit and Dayvilo multiplies your value by seven before adding or subtracting, which is handy for planning deadlines a set number of weeks away.
Months use calendar-month arithmetic. Adding one month moves to the same day in the following month whenever that day exists. This keeps results predictable across months of different lengths.
One year equals twelve calendar months, so the Years unit lands on the same calendar date in the target year whenever it exists. September 1, 2026 plus 1 year is September 1, 2027, and minus 1 year is September 1, 2025. A February 29 start clamps to February 28 in non-leap target years, so February 29, 2028 plus 1 year becomes February 28, 2029.
When the target month is shorter than the start day, Dayvilo clamps the result to the last valid day of that month instead of overflowing. January 31, 2027 plus 1 month becomes February 28, 2027, and January 31, 2028 plus 1 month becomes February 29, 2028.
Every calculation respects leap years. February 29 exists only in leap years, so month arithmetic that lands on it in a non-leap year clamps to February 28, and day arithmetic counts February 29 whenever the year includes it.
Pick a start date, enter a value, choose Days, Weeks, Months, or Years, and select Add or Subtract. Dayvilo shows the resulting date and its weekday instantly.
Months and years use calendar arithmetic with end-of-month clamping, and one year equals twelve months. If the resulting month has fewer days than the start day, the result clamps to the last day of that month. For example, January 31 plus 1 month is February 28, or February 29 in a leap year, and February 29, 2028 plus 1 year is February 28, 2029.
One week always equals seven calendar days, so choosing the Weeks unit multiplies your value by seven.
Yes. Leap years, February 29, month boundaries, and year boundaries are all handled correctly for both adding and subtracting.
The value must be a whole number of zero or more. If you enter a negative or non-whole number, Dayvilo shows an inline message. Use the Subtract operation to count backward.