Calculate monthly percent

Question

In credit system, client take a debt money for %3 monthly and he must pay same monthly debt in every month to close his debt.

I need to find that same monthly debt in every month. I can not find that, how they find the 221.02. I have one sample:

Amount = 2200
Month count = 12 month  
Monthly percent = 3 %

In this case we get this table:

     amount      %3 percent      net debt       monthly debt
 1.    2200          66.00         155.02           221.02
 2.    2044.98       61.34         159.67           221.02 
 3.    1885          56.55         164.46           221.02
 4.    1720.85       51.62         169.39           221.02
 5.    ......        .....         ......           221.02
 .........................................................
 12.   214.54        6.43          214.54           221.02

In this sample, client pays 221.02 for every month and after 12 month debt finishs. Calculations is like this:

For fist month, we find (2200*3/100)=66 and 221.02-66 = 155.02. In second month: 2200-155.02 = 2044.98 and continues.

We see in example,

For 2200 amount, for 12 months, monthly debt is 221.02. 
For 2200 amount, for 6 months, which monthly debt will we get?

Generally, if we know amount, percent and month count, how can we calculate monthly debt (same value in every month) in c#?

Thanks in advance.

Answer 1

A series of payments at regular intervals is an annuity. The division of a sum into such is called amortization. To determine the fixed amount, divide the sum by the present value of the annuity.

Here's how you can calculate the present value of an immediate annuity at interest i per period over n periods in Clojure, a functional language.

(defn pv-annuity [i n] 
  (let [v (/ 1 (+ 1 i))] 
    (apply + (take n (iterate (partial * v) v)))))

This says, the present value is the sum of the present value of each payment, 1/(1+i), 1/(1+i)^2, 1/(1+i)^3, ..., 1/(1+i)^n.

The desired fixed payment is then

(/ 2200 (pv-annuity 0.03 12))
;=> 221.0165880405186

Answer 2

I believe this is what you are looking for

Financial.Pmt

If not look in the Financial class