math - What is the Mathematical formula for CUMIPMT function of EXCEL(how it is calculated)?

Question

What is the Mathematical formula for CUMIPMT function of EXCEL(how it is calculated)? I want to calculate it mathematically. Please Help

Answer 1

The implementation of CUMIPMT in Excel is impossible for us to provide seeing as Excel is not open-source.

However numerous results show up in a Google search such as this implementation in Javascript, this other implementation also in Javascript, or PHPExcel's implementation in PHP.

The closest result would probably be to look at Open Office's C++ implementation - thats very close or identical to Excel's implementation.

It's available in the OpenOffice repository on Github

double SAL_CALL AnalysisAddIn::getCumipmt( double fRate, sal_Int32 nNumPeriods, double fVal,
    sal_Int32 nStartPer, sal_Int32 nEndPer, sal_Int32 nPayType ) THROWDEF_RTE_IAE
{
    double fRmz, fZinsZ;

    if( nStartPer < 1 || nEndPer < nStartPer || fRate <= 0.0 || nEndPer > nNumPeriods  || nNumPeriods <= 0 ||
        fVal <= 0.0 || ( nPayType != 0 && nPayType != 1 ) )
        THROW_IAE;

    fRmz = GetRmz( fRate, nNumPeriods, fVal, 0.0, nPayType );

    fZinsZ = 0.0;

    sal_uInt32  nStart = sal_uInt32( nStartPer );
    sal_uInt32  nEnd = sal_uInt32( nEndPer );

    if( nStart == 1 )
    {
        if( nPayType <= 0 )
            fZinsZ = -fVal;

        nStart++;
    }

    for( sal_uInt32 i = nStart ; i <= nEnd ; i++ )
    {
        if( nPayType > 0 )
            fZinsZ += GetZw( fRate, double( i - 2 ), fRmz, fVal, 1 ) - fRmz;
        else
            fZinsZ += GetZw( fRate, double( i - 1 ), fRmz, fVal, 0 );
    }

    fZinsZ *= fRate;

    RETURN_FINITE( fZinsZ );
}