Overpaying mortgage

[Livvyliv18]

If you overpay your mortgage every month how do you do it and how much do you over pay ?
Ive increased my DD by £100 and then I add the odd £50 when I have spare cash.I also round up my bank account every night.It works out Im probably overpaying about £250 pm.
Would it be better to pay larger amounts at a time or is it ok to trickle money in?
The balance never seems to go down!
My mortgage company allows up to 10%.
Ive looked at the overpayment calculators so I know it’s worth doing but I’m just unsure if I’m doing it the best way
TIA

I'm with Santander and overpay each month
I phone up to do it and they ask if l want to reduce the capital or term.

I then receive a letter with the new mortgage amounts

I don't overpay as savings rates are higher than the interest rate on my mortgage now. I will pay lump sum when I remortgage in a few years time.

@iRun2eatCake if you have the Santander app you can overpay on there. Might save you the hassle of a call.

Alas l have more then one part to my mortgage so it won't allow me too.

Would save me so much time if it did!