Interest calculations

This is a simple spread sheet for calculating daily Bank or Mortgage balances with various interest rates.

If interest is credited or debited on a daily basis and if it is assumed that there are 365.2425 days in an average year, and interest is expressed as the annual percentage rate (APR), then a financial statement would take this form: NB = PB * ((1 + (APR/100) ^ (days/365.2425) + C - D

Where NB = the "new balance" .

PB = the “previous balance".

APR = the annual percentage rate during the intervening period.

* is multiplied by, + is plus, - is minus & = is equals

^ is to the power of (e.g. 2^3=8 or 2*2*2=8)

"days" is the number of days since the previous transaction (i.e. between PB and NB)

365.2425 is the average length of a civil year in days (This is the Gregorian correction allowing for a leap year of 366 days when the year is divisible by 4 but not by 100 unless it is also divisible by 400).

C = a credit.

D = a debit.

This spread sheet does these calculations for you: