Recently, I met with one of my best friends, who is trying to follow in my footsteps and retire before 50. Our conversation eventually turned to mortgages. Because apparently this is what happens when you get older. She was considering making extra payments toward her mortgage principal. You've probably heard the advice before: Make one extra mortgage payment a year, and you'll shave years off your loan. I'd heard an even more impressive version a few years ago on YouTube. An