How it works
Both loans are computed on the same principal and the same remaining term, so the only difference is the rate. That keeps the comparison honest: a new loan over a longer tenure would show a lower instalment while costing more in total, which is how transfers are often mis-sold.
The switching cost is the processing fee on the new loan, any foreclosure penalty on the old one, and the fixed legal and valuation charges. All of it is payable upfront.
More detail
The break-even is that cost divided by the monthly reduction in instalment. It is the number that decides the question, because a transfer that takes forty months to repay itself on a loan with thirty months left is a loss dressed as a saving.
Where the new rate does not reduce the instalment at all, no break-even is reported rather than a meaningless figure — there is nothing for the cost to be repaid from.
To compare against simply prepaying instead, use the prepayment calculator.
To find what you actually still owe, see the loan balance calculator.
To see what a different tenure would do, try the home loan EMI calculator.