A fixed or discount rate deal can apply for anything from just a few months to your entire mortgage term (e.g. 25 years). Once the deal is over you will be transferred over to the lenders standard variable rate so choosing how long the discount or fix applies for is an important decision.

Short Deals 
 
The most attractive discounts or fixes will often only last for short periods – for example one or two years. However, these deals usually come with an extended redemption penalty so that the lender can make back the money lost through the attractive initial rate by keeping you stuck on their uncompetitive standard variable rate for several years.
 
They therefore are unlikely to offer any real savings and should only be chosen if you are currently struggling to find the payments but are certain that you will be in a better financial position once the deal comes to an end.

Long Deals 

At the opposite extreme you may be tempted to opt for a very long deal, such as ten or fifteen years. This will mean you know exactly how much money you will have to find each month for a long time into the future.
 
The wisdom of such a move will depend on where interest rates go – if interest rates rise sharply then it could prove very astute and leave you paying much less than you would otherwise.
 
However, if interest rates fall you could be stuck on an uncompetitive rate for a very long time or face paying a very hefty early redemption penalty to switch your mortgage to a better rate.

Medium Term Deals  

The vast majority of borrowers opt for medium length deals of between two and five years and this is likely to be the best option for you unless you have a very strong opinion about the future direction of interest rates.
 
These give you some flexibility while also ensuring that you are not constantly remortgaging.
 
The exact length of time you opt for will depend on your individual circumstances.
 
When choosing shorter deals you need to weigh up the additional costs and time involved in remortgaging, which you are likely to want to do at the end of the deal so as to avoid being transferred to the lenders standard variable rate
 
When choosing longer deals you need to take time to think about the possibility of changes in interest rates and how this may affect the competitiveness of the deal you have chosen.