One way...............

enter in B4 ....=30-(TODAY()-40116)/30
40116 is the number for today the 30th of october
tomorrow the formula will give you
30 -(40117-40116)/30
or
30 - 1/30
the day after it will be
30 - 2/30

you can format the cell to have a few decimals to see where you are.
or you can add a "round()" function if you need whole numbers
The second part of your question would have to be done with a macro and you
would need to specify when or how often. I.e. check once per day?

Greetings from New Zealand

"Flyboy" wrote in message
...
Need to be able to have cell B4 decrease by 1 every 30 days until it
reaches 0

I would also like to be able to take values in A17 move up one if A16 is
empty.