Calculate Interest payments in loan repayment schedule

[GINMED]

Hi,

I need your support in Beginning balance and Ending balance calculations!

I have stucked with interest payment because there is first payment indicated as amount.

How can I put such calculation in Beginning and Ending formula?

There is my calculations but it is wrong in such scenario.

Beginning Balance =

Var PV = sum('Līgumi'[PV])

Var Interest = SELECTEDVALUE('Līgumi'[Rate in period])

Var Index = SELECTEDVALUE('Project'[Sequence])

Var Payment = MIN('Līgumi'[Rent payment])

Var Result =

             if(PV *

                     POWER( 1 + Interest, Index - 1 ) - Payment * DIVIDE( POWER( 1 + Interest, Index- 1 ) - 1 , Interest) >= 0,

                PV *  POWER( 1 + Interest , Index - 1 ) - Payment * DIVIDE( POWER( 1 + Interest, Index- 1 ) - 1 ,Interest),0) RETURN Result

Ending Balance = if([Beginning Balance] - ([Payment] - ([Beginning Balance] * sum('Līgumi'[Rate in period]))) >= 0, [Beginning Balance] - ([Payment] - ([Beginning Balance] * sum('Līgumi'[Rate in period]))),0 )

I allready calculate interest with FIRST payment, but I dont know how correctly to put it in Beginning and Ending calculations.

There is my sample data.

Thank you in advance,

GINMED