Savings calculation? Help?

[jim lee]

Hello everyone,

I'm trying to model a savings account. Two tables, Accounts and their related transactions. The sum of the transaction amounts give the account balance. Simple enough.. But how to calculate a compounded interest?

My thought was to add an interest transaction each time something changed either the interest rate or the addition of a transaction. But I can't find a formula for calculating compunded interest.

I have

Interest rate

The startting balance

The amount of time

All the functions I see have you putting in payments. This is just one lump sum over time.

Many thanks in advance!

-jim lee

[comment]

There are two ways to compound interest: periodically and continuously.

The future value of a deposit with periodically compounded interest is:

principal * ( 1 + rate )^nper

where rate is the interest rate PER COMPOUNDING PERIOD, and nper is the number of compounding periods.

The future value of a deposit with continuously compounded interest is:

principal * Exp ( rate * nper )

where rate is the interest rate per any arbitrary period, and nper is the number of those periods.

[jim lee]

Thank you!

That was -exactly- what I was looking for.

-jim lee