Paying Mortgage Off Early

Hey all. My husband and I bought our home in 2019, and we just renewed our mortgage for another 5 years (starting amortization was 25 years). We've always paid bi-weekly to get in tgat extra payment, and we've thought about making an extra payment on principal only when my car loan is paid off next month. I heard if you make that one extra payment on the pricipal, you can shave 5-7 years off your amortization, which sounds ludicrous. When I used a prepayment mortgage calculator, it shaved about a year off our mortgage. Does that mean it's only reducing it by a year if we made an extra payment every year? Sorry, I sound dumb but I've seen lots of videos on YouTube and don't know how they're getting those results.