Small adjustments, applied early and kept up, shorten an amortization by years.
Every dollar applied to principal reduces the balance on which interest is calculated for all the years that follow. That is why a modest effort at the beginning is worth far more than a large one at the end.
The four levers
Change your payment frequency. Moving from monthly to weekly or biweekly accelerated is equivalent to making one extra monthly payment a year, without it showing up in your budget. Watch for the word accelerated: without it, the effect is not the same.
Increase your payment amount. Most contracts let you raise your payment by a set percentage each year. Doing it when you get a raise is painless: you had not yet built the habit of spending that money.
Make lump-sum payments. A bonus, a tax refund, an inheritance. Most contracts allow an annual prepayment up to a percentage of the original amount, penalty free. Applied to principal, the effect is immediate.
Keep the same payment at renewal. If your rate drops at renewal, keep the payment you had. The difference goes straight to principal and nothing changes in your lifestyle.
Check your privileges first. The percentages allowed, the dates permitted and the penalties for exceeding them vary a great deal from lender to lender. That is one more reason to compare conditions and not only rates when you sign.
Is it always the best idea?
Not necessarily. If you carry debt at much higher rates, such as credit card balances, paying those off generally comes first. And if you have no emergency fund, building one before accelerating your mortgage is usually the wiser move. I am not a financial planner, but I will tell you if an extra payment looks premature in your situation.