There are no hard and fast rules that you can apply to the situation regarding early repayment charges on any particular type of mortgage. You really need to double check the specifics of your mortgage.
Your original mortgage offer should detail the early repayment charges that will apply, both in terms of how long they apply and the method of calculating any applicable charge. If you can’t find that, call your lender.
Lots of mortgages will now allow partial repayment of the mortgage without any penalty, even during an early repayment charge period.
Although it will vary from lender to lender and even deal to deal, it will typically be around 10% of the outstanding balance.
Some deals don’t impose early repayment charges at any time and that is more likely to apply to a base rate tracker, but is certainly not guaranteed.
If you’ve reached the end of a deal, fixed or tracker, and gone on to the lender’s standard variable rate then there is a good chance that you will not face a penalty for paying off a lump of your mortgage.