How it works
Start from any date and add or subtract years, months, weeks and days. Adding months keeps the day of the month where it can and otherwise lands on the last day: 31 January plus one month is 28 February (29 in a leap year).
Questions and answers
What date is 90 days from today?
Open the Add or subtract tab, keep today as the start date and enter 90 days; the result updates as you type.
What happens when I add a month to 31 January?
You get the last day of February, because February has no 31st.