Add / Subtract Days to a Date

Calculates a new date when you add or subtract a certain number of days to a date. The current date is preset. Use this or another date, insert the amount of days and choose, if you want them to add or to subtract. The new date will be calculated. The different lengths of the months as well as leap years are taken into account. The result can then be used for further calculations by pressing Result in row 1, delete row 2.

Calculating with days and calendar dates is so difficult because months have different lengths and years can also vary. Months have between 28 and 31 days. Most of them, 7 months have 31 days, 4 months have 30 days and one month, February, usually has 28 days, and in a leap year 29 days. Accordingly, the year usually has 365 days. In a leap year, approximately (but not exactly) every four years, it has 366 days. If you add or subtract a number of days that takes you to a different month, then the calculation requires a lot of mental effort - the longer the span, the more.

Day and year are based on astronomy. A day is the time it takes for the earth to rotate around itself until it shows the exact same side to the sun again. In a year, the earth orbits the sun once and then returns to the same point on its orbit. The month, on the other hand, originally referred to the duration from one lunar phase to the next, for example from full moon to full moon. In reality, this duration corresponds to about a month (a little less, namely about 29.5 days), but since the lengths of the months are different, the months have now become decoupled from the moon.