How Excel stores dates

Dates are numbers in disguise. Build them with DATE, take them apart with YEAR, MONTH and DAY, and move them with plain arithmetic. Beginner · 5 min · Serial numbers, DATE, YEAR / MONTH / DAY, TODAY

Behind every date in Excel is a whole number called a serial number: the count of days since January 1, 1900. January 1, 2026 is day 46,023. A date format just dresses that number up so people can read it.

Because dates are numbers, you can do arithmetic with them. Add 30 to a date and you get the date 30 days later. Subtract one date from another and you get the days in between. The sheet below lists upcoming bookings at an event venue.

> If a date suddenly turns into a five-digit number, nothing is broken. The cell has just lost its date format.

Steps

The venue's booking form saved each event date as three separate numbers. In E2, join them back into a real date with =DATE(B2, C2, D2), then fill it down to E7.
Time to peek behind the curtain. B9 has no date format. Type =E2 there to see the number Excel actually stores for the Okafor wedding.
Invoices are due 30 days after the event. In F2:F7, add 30 to each event date.
Clients get a discount if they rebook the same date next year. In G2:G7, take each event date apart with YEAR, MONTH and DAY, add 1 to the year, and put it back together with DATE.
Last one. In B10, type =TODAY() to show today's date.

Remember

Dates are serial numbers: days counted from January 1, 1900.
=DATE(year, month, day) builds a date; YEAR, MONTH and DAY take one apart.
Add or subtract whole numbers to move a date by days.
=TODAY() always shows the current date; Ctrl+; types a fixed one.

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