This calculator is designed to be played with - enter your interest rate and gfind out how much you can expect to pay each month to pay the loan off over 25 years.
Try different numbers until you get a number in year 24 and a zero in 25. (At this point it means that your mortgage will terminate during the last year).
Then put in the maximum you might be able to pay each month into the calculator and see what a difference it makes to the overall payment and time taken to buy your house.
In practice you do not have to commit to this higher amount every month - simply setting money aside and putting it in as a capital reduction when you can spare it will have the same effect. (This may be of particular note to those who have special deals that penalise early capital repayment).
Note - surprisingly small accelerated payments can shorten the mortgage by several years and lead to savings of thousands of pounds.
Cheat - for a £100,000 mortgage at 10% interest try 878.5 in the 25 year column and 1100 in the accelerated one.
Interest - for mathematical purity the interest is calculated on the basis of the twelth root of the rate selected, and the outstanding capital recalculated each month. In practice mortgage maths is different in detail and so do not expect these figures to match those of any quote.