Dates, counted properly.

Counting days between dates, and adding days to one

Two questions get confused constantly: how many days lie between two dates, and what date it will be N days from now. They use the same numbers and give different answers, so the tool separates them.

1. For the gap between two dates enter the earlier date and the later one. The result is the number of days between them, plus the equivalent in weeks and months. This is the shape used for notice periods, project timelines and how long until something happens.
2. For a date in the future or the past enter a start date and a number of days with a sign: 90 forward gives a date about three months out, −30 goes back a month. This is the shape used for "net 30" payment terms and for return windows.
3. Watch the difference between inclusive and exclusive counting From the 1st to the 8th is 7 days if you count the gap, and 8 days if you count both ends. A hotel night is a gap; a holiday is usually counted inclusively. The tool reports the gap, which is what contracts and interest calculations mean.
4. Check the weekday. The result includes the day of the week, because "30 days from Friday" landing on a Sunday is the kind of detail that changes a deadline.

When this comes up

• Notice periods and contract terms. "Thirty days from the date of this letter" needs an exact date, and counting on fingers across a month boundary is how people get it wrong.
• Return windows and warranty periods. Retailers count from the delivery date, not the order date, and the difference is often the whole dispute.
• Project planning. Working backwards from a deadline to find a start date, or forwards to check whether a timeline is realistic.
• Age in days. For visa applications, insurance quotes and anything that asks how long someone has been alive or how long an account has been open.

Questions