IPMT(rate,per,nper,pv,fv,type)
IPMT calculates the amount of a payment of an annuity going towards interest.
Formula for IPMT is:
IPMT(PER) = -PRINCIPAL(PER-1) * INTEREST_RATE
where:
PRINCIPAL(PER-1) = amount of the remaining principal from last period
PPMT, PV, FV.