If I overpay up to the 10% annual limit, do I HAVE to reduce monthly payments or else fees?

getmore4less

bagpussofsussex said:

OOh I didn't know that was a thing with Halifax... My endowment matures next year (from my first mortgage). So to avoid them adjusting my monthly payment, I need to work out 10% of the balance on Jan 1st, then 12x my regular monthly overpayment, and make my lump sum overpayment no bigger than the difference between the two? And then bank the rest of the endowment money until the next calendar year...

Why bother?
Overpay as much as you can as soon as possible that saves more than trying to keep the payment the same with smaller lump overpayments.