Aiming for mortgage freedom in 5 years

sgc21

I have a new 12yr remortgage fixed for 5 yrs starting June 23 going to try hard to get it paid off within the 5 yr fixed term, I have the over payments on a spreadsheet that i knocked together and as the mortgage decreases with overpayments I find that I can't pay as much as I'd like due to the 10% overpayment rule, so thinking I need to put the rest of the overpayment in a savings account so I can use it to pay off the balance after 5 yrs.

Anyone know of any good spreadsheets templates to calculate overpayments accurately?

mortgage Balance 74,500
Rate 4.5
Monthly cost 650

Year 1 overpayment 430
Year 2 overpayment 500
Year 3 overpayment 385 / saving acc 250
Year 4 overpayment 282 / saving acc 414
Year 5 overpayment 189 / saving acc 464

Hoping this gets me mortgage free in 5 years any tips or advice?

Thanks