Every refinance advertisement leads with the rate. Almost none of them lead with the month at which you actually start saving money, which is the only figure that decides whether the exercise is worth doing.
The arithmetic
Take the total cost of moving — arrangement fee, valuation, legal work and any early repayment charge on the loan you are leaving. Divide that by the monthly reduction in your payment. The answer is the number of months before you are ahead.
If that number is larger than the number of months you realistically intend to stay in the property, the lower rate is costing you money. This happens far more often than the adverts imply, particularly where an early repayment charge is still running.
When it is worth doing anyway
Shortening the term, moving off a standard variable rate, or releasing equity for a purpose that earns more than the borrowing costs are all reasons that survive a bad break-even. Chasing a quarter point is usually not.
