your annuity is earning you 2% per year compounded monthly.
you are withdrawing the money at the end of each month.
the following online calculator shows you how to do it.
the calculator can be found at http://arachnoid.com/finance/
you would enter:
present value = 0
future value = 0
paymnt = 200
interest rate percent = 2/12 = .1666667 per month
number of months = 12 * 20 = 240
you would select payment at end of time period.
you would click on pv and you would get pv = 39,534.79 as shown in the following picture.
disregard the sign.
it has to do with cash flows in or out.
the pv is a cash flow out because you take your money and put it into the annuity fund.
the payment is positive because you are receiving money from the annuity fund.
a key point is that you need to determine the interest rate per time period and the number time periods.
your time periods are in month because the payments are monthly and the interest rate compounding is monthly.
you take the annual percentage rate and divide it by 12 to get the interest rate percent per month.
you take the number of year and multiply them by 12 to get the number of months.
the calculator does the rest.
there are formulas involved so that you can do the work manually by using the formula.
they can be found here:
https://www.algebra.com/algebra/homework/Finance/THEO-2016-04-29.lesson#notes
the formula you would be looking for would be:
PRESENT VALUE OF AN ANNUITY WITH END OF TIME PERIOD PAYMENTS
when you are using the formulas, you need the interest rate and not the interest rate percent.
2% interest rate percent is equal to .02 interest rate.
.166666667 interest rate percent is equal to .00166666667