There are 4 methods of payment: annualy, quarterly, semestrial and monthly. For all of these methods we calculate a number of installments (to pay) by the end-user.
First 3 years are presented like in the picture.
Starting with the 4th year, the promotional plan is no longer valid, so the rest of the payment plan is like the annual one.

Please help me out and advice me how can i calculate the whole payment plan

I have just filled in the date, i wasn`t aware of these instructions on this forum. Thank you for the tip! Maybe you could help me out a little with this calculation, my work depends on it and i`ve been strugling two weeks now...unfortunately.

Basicly i need that starting from the first rate from the 4th year, the calculation is the same as the (normal one). First three years are on (promotional formula)
How can i insert a function which allows me to change the used formula, starting from the 4th year, to give another formula ( there are 4 ways of payment as in the picture- so the first rate in the 4th year can be in rates 3,7,17,37).

Thank you, kind regards