EMI is made up of two variable components- principal amount and interest rate. The EMI is fixed but not the components. The component of interest amount is higher in initial years and decreases over the years. The component of principal amount is lower in initial years and increases over the years.
For this reason, if you consider pre-payment, you should do it in early years as you save on interest rate.
EMI (Equated Monthly Installment) calculation formula :
EMI : Equated Monthly Installment
Principal : Loan Amount
ROI : Rate of Interest [Monthly basis - Ex. 13.5 p.a = 13.5/100/12 = 0.01125 ROI]
n : no of months
Monthly Interest Adjust : Begining Balance x ROI [Ex. 2,500,000 x 0.01125 = 28,125]
Monthly Principal Adjust : EMI - Monthly_interest [Ex. 38,069 - 28,125 = 9944]