Rookie Refinance Question

[Vanessa Marchand]

I'm almost embarrassed to ask (well, I AM embarrassed to ask) having had a 20 year stint in banking. When you refinance your loan to get a better rate, your amortization resets and you're back to square one as it relates to the interest/principal split. My goal is to buy and hold single family houses for 20ish years at which point I will likely sell off the portfolio. During that 20ish years I'm going to assume rates will fluctuate and maybe to a point where it would make sense to refinance one or more of the 30-year fixed mortgages on these homes. I am having the DARNDEST time wrapping my head around how to determine the breakeven point. I can do the simple math, of course, to find out the break even point on the rate reduction benefits and the refi fees. But let's say I've had one of the loans for 5 years and one for 10 years before rates drop enough to make a difference in payment. By that time, the principal portion of my payment will have increased from let's say 12% at the start of the loan to 17%-25% after those 5-10 years. If I refinance, sure my monthly payment will go down and the cash flow on my properties will improve but I'm losing that interest/principal split on my loans. In my mind, there's another simple calculation I need to do to figure this out but I just can't get there! I've spent my fair share of time in excel creating these amortization schedules and my mind is fried. Does anyone have a tool that I can use to help?