How do i figure monthly intrest, principal, per diem, and current balance on excel?

i need like a formula to put in and not all the monthly payments are equal or on time. Im trying to find the balance of monthly payments that are being made to me and i am the one that keeps tract of them and collects payments so no one else has the info but me. but the spreadsheet needs to show the intrest, per diem etc. thanks!!!|||Its easy... you have to make your own formulas... I could make one for you but its too complicated to write in here. But basically you put your beginning balance * interest rate = interest payment + principal payment. then you get a new balance and put that amount under the beginning balance and so on.