How to have a number deduct from another automatically each day

SO what im trying to do, is Have a balance automatically deduct a predefined number each day.

E.g -5000 each day. So first day it would be for example 20000, then once a day has elapsed, it deducts 5000 from 20000 giving 15000, then following each day it deducts 5000 again so on and soforth.

I have tried today() but it does not allow any arguements, wasnt able to really understand any other formula, DATEIF converts date to a number but it only goes up by 1 each day not allowing for that date string to be modified, or for any way to have +1 in the dateif deliver a -5000 into another cell. kind of lost so hopeing someone can help!

Thanks!