Add or Subtract Dates in Google Sheets

If you want to subtract one date from another in Google Sheets, simply make sure that both dates are actually in the date format by clicking “Format”, “Number” and “Custom date and time”. Then choose the date format you prefer. Then dates can be subtracted from each other without any problem.
This can be used to create a count down timer by using the function =TODAY() and subtract this date from any future date we are looking forward to. Then the result will always be the number of days left until that date.
If you instead want to add days to a date to check what the future date will be, this can be done by adding a number that corresponds to the amount of time in days to the future date.