"What date is 100 days from today?" "My contract ends three months from signing — when exactly?" "What was the date 45 days ago?" Pick a starting date, an amount and a unit, and get the exact target date with its day of the week. Both directions work.
The month-end rule
Adding months follows banking convention: if the target month has no matching day, you get the last day of that month. January 31 plus one month is February 28 (29 in a leap year). Day, week and year arithmetic adds calendar days with no special cases.
Common uses
Returns: most stores allow 30 days from purchase. Trials: 14 or 30 days after signup. Fitness memberships: 365 days from activation. Deadlines: 45 or 60 days after notice. Pair it with the Date Difference Calculator to verify both ends agree.
Frequently asked questions
What is 100 days from October 1, 2026?
Set the start to 2026-10-01, add 100 days and you get January 9, 2027 (a Saturday).
Why does January 31 + 1 month give February 28?
February has no 31st, so the result snaps to the last day of February — the same rule banks and billing systems use.
Can it count business days instead?
This tool works in calendar days. Use the Business Days Calculator for Monday-to-Friday counting.