Draguen wroteHey, in those cases, use Excel:
Take a basis value of 100 000, multiply it by 1.05 and remove 10 000: at the end of the first year you will have 95 000.
Now use the same formula but replace 100 000 by 95 000 and click and drag on excel. After 14 years you will be left with 2000 dol, after 15 years, you will have a debt of 7892 dol.
I can explain more in details if you need, but I'm on my phone for the moment
That is not the easy way to do it--you can find calculators online to do this for a lot less effort. Look for annuity payout calculators. In this case, given 100k current value, 20 years to pay out earning at 5%, you can withdraw a bit over $8k per year before the money runs out.
http://www.calculator.net/annuity-payout-calculator.html
It can be done in excel in a much easier fashion, but I can't recall how to do it right now.
Edit: remembered
For your example use =pmt(.05,20,100000,0)