spreadsheet for accruing interest and penalties that vary

[Dean]

Trying to create a spreadsheet that calculates compounding interest and
penalties, where the interest rates change per quarter.

 

[Fred Smith]

How often is interest compounded? Daily? Monthly? Quarterly? Annually?
How often do you have transactions which affect the balance?

Whether you have many transactions per period (such as a credit card bill),
or many periods per transaction (like a long-term investment), will make a
difference in how you set up the spreadsheet.