Should I make prepayments to eliminate ROI?

[Kelvin He]

Hello, 

I just bought a house w/ a mortgage of 30 yrs. + 4.5% interest rate, 3% down. The loan amount was for 235k.

My P&I = 1,194 / mo

PMI = 86 / mo

If I don't make prepayments, then I can get rid of PMI in 10 years..

How do I calculate whether or not I should make prepayments to get rid of PMI? IRR? I want to compare it to other ways I can invest that money if I didn't put it down on principle. Thanks!