Determining Differences Between Dates

@ Karim K….See also here: http://www.excelfox.com/forum/showthread.php/2345-Appendix-Thread-(-Codes-for-other-Threads-HTML-Tables-etc-)?p=12309#post12309 ….

Hello Karim K. ……
One way would be to have a macro that starts running every time your workbook is open. That could check the date in any cells of your choice for a date, say, column C, and if found do your required calculations and produce your required results.
…. .
It could be written in such a way that macro also runs every time you type a new date in column C
….
For example, open this workbook. : https://app.box.com/s/ti0n1wj62hcd2qmhcg5kiqle1sya79ux
…..
…
It will put the count you want alongside in column D, and a few other things based on Allen Wyatt’s notes above and a few other things I felt like doing.
……
Alan Elston
…
(P.S. I am taking a guess that you meant 2/15/2020 to give you a 1 , not 2/15/2019)

I am trying to let the user input a Date in a cell. Using the input date and today's date, I would calculate how many days have passed since the user's input date.

Example: User inputs "2/15/2019" in cell (C4) - The next day it shows "1 Day/s" and so on.

I've searched and tried many things but failed, I am no expert with excel or VBA by any means, so I am not even sure if that is possible.

Datedif() ALSO has 2-3 failures available. 2-3 of the options give wrong answers.

This is a known defect and lack of interest by Excel in fixing it is probably why they don't document it. Likely they left it in though for any spreadsheets written using it by trusting souls. Those souls only had to fix the formulas that used the defective operations.

I don't remember the defective options off-hand but I'm sure the internet does:

https://support.office.com/en-us/article/datedif-function-25dba1a4-2812-480b-84dd-8b32a451b35c says the "MD" option may give wrong naswers. It also says it was intended for compatibility with 1-2-3.

Other sites add information and it looks like it picks the second month entered as "the" month toi base to calculation on which causes difficulties if the two months involved do not have the same number of days. For example, February and any other month will cause 2-3 days to be added to the answer expected if January is the month of the second date. And vice versa. And some palces suggest it is less straightforward than that, either way, it is not only an obvious difficulty programmers should have expected (and MAY have, but kept it so because the 1-2-3 function worked (worongly) that way - or not, maybe the 1-2-3 function worked perfectly).

In any case, it has at least the one defect and I seem to recall there was a second, but you know how recall goes as one gets old...

In any case though, most all of it works so if ya wanna use it, it's there to be used!

Just a caution...

When working with dates, always consider the possibility that your date serial numbers may have fractional portions. That's because everything to the right of the decimal point represents time with a given integer date. It's very slick.

Some examples of date serial numbers and what they represent:
43689.000000 August 12, 2019 -- specifically at 12:00 midnight at the start of the day.
43689.500000 August 12, 2019 at noon
43689.750000 August 12, 2019 at 6:00 pm (18.00)
43689.999988 August 12, 2019 at 11:59 pm (23.59.59)

Depending on your needs and your data, it may be good to truncate date values to make them integers before subtracting one from the other.

Also, when working with dates, you need to decide whether to add one to the result or not, depending on your needs.

For example, if both of your dates are August 12, do you want your result to be zero days or one day? Merely subtracting the values will give you zero days, but that may not match your intent. In that case, modify your formula to add 1 to the result.

Similarly, if your two dates are August 12 and 14, do you want the result to be 2 days of 3?

Datedif is also available as a worksheet function (at least up to Excel 2013). MS stopped documenting it early on, for some reason, but it has remained in the product. The syntax is different:
= Datedif(<first date>, <second date>, <format>), where 'format is "Y" for years, "M" for months, "YM" for months ignoring full years, and "MD" for days ignoring full months. A formula of:
=DATEDIF(H16, H22, "Y") & " Years, " & DATEDIF(H16, H22, "YM") & " Months, and "& DATEDIF(H16, H22, "MD") & " days"

will return a result like:
3 Years, 2 Months, and 20 days