Small changes add up
Why a little extra goes so far
Interest is worked out on what you still owe. Knock some off the balance today and you are not charged interest on that money again, in any month for the rest of the loan. That is why $100 paid now saves far more than $100.
How to read the result
Put in the extra you can really manage and compare it with the plain schedule. The tool rebuilds the payment plan month by month, trims the last payment to whatever is left, and shows the new end date and what you saved.
Try it before you commit
Test an amount you can keep up every month, a yearly bonus, and a one-off payment. Then ask what else that money could do. Savings for emergencies come first. So do debts that charge you more than the mortgage does. If your employer matches money you put away for retirement, take that too.
Tell your lender what it is for
Check how to mark a payment as going onto the balance, and whether your loan charges a fee for paying it down early. Some websites quietly move your due date forward instead, which is not what you want.