Vba to calculate interest, penal interest etc

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VBA

I have an excel file:
A1= Date of loan payment
B1= Amount of loan paid
C1= Rate of interest
D1= Rate of penal interest
E1= Total allowed instalments
F1= Interval in months for each instalment. 3 if its quarterly so and so
G1= Date of first instalment due

So, B1/E1 will be single instalment amount. So on each due date (depends on F1) one protion of principal will be due, must calculate interest, and from next instalment, if principal is over due then penal interest also to be calculated.

Can any one help me to get a code which will check each line (each line will be seperate loan payments) and to get the due amount of principal, interest and penal interest

What I have tried:

Tried lot but confused.
Lot of method tried, but after all i fail. so if anyone can help me from scratch i will be much happy