# Discounted Cumulative Interest Calculation in One Cell

#### bran8989

##### New Member
I am trying to discount cumulative interest over a period of time.

Say I have an original mortgage for \$100,000 and a term of 60 months, then the borrower prepays on month 1 for \$50,000. I want to know what the cumulative interest lost over that period is at a discounted rate of 15%.

I want to do this without having to build an amortization table, ideally want to do it using a formula in one cell.

Thanks

#### James006

##### Well-known Member
Hello,

Which formula are you using to calculate interest ...???

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#### bran8989

##### New Member
I'm using CUMIPMT.

#### bran8989

##### New Member
The problem I'm having is CUMIPMT is really just the combined cumulative interest undiscounted. What I really need is a way to discount each period of lost interest then sum the total.

#### James006

##### Well-known Member
Hi,

In terms of the formula you are using to calculate interest ...

1. Do you have a fixed annuity ...

2. Or is it interest on remaining outstanding capital ?