Standard mortgage terms in the UK are typically 25 years, but you can get a mortgage that lasts between 6 months and 40 years. For example, if you took out a 25-year mortgage in 2010 and made all of the repayments, it would be fully paid off by 2035. If you are getting your first mortgage:

A term of less than 20 years is considered to be a short-term mortgage
A term that is 30 years or more would be a long-term mortgage
However, when it comes to fixed interest rates long-term fixed rate deals have been quite rare since the 2008 financial crisis as lenders have become increasingly risk averse. So, in terms of 20-year fixed mortgage rates you may struggle to find a good offer from a lender, but it is still worth researching and seeing what is available to you.

When comparing mortgages for the same amount borrowed, but over different time periods, longer term mortgages generally cost less per month because the repayments are spread over an extended term. However, you will pay more overall because you are charged more interest when you have a mortgage over a longer term.

Shorter term mortgages for a same sized mortgage will cost more each month but let you pay the balance off quicker. Therefore, you will own your home outright much quicker and pay less overall because you are charged less interest.
Everyone’s financial circumstances are different and what may be suitable for one person might not suit someone else. So, the most suitable mortgage term is one that gives you affordable monthly repayments but does not have you paying more interest than is necessary. 20-year mortgages will give you slightly higher monthly payments so make sure you can fully afford them before you commit but you will pay less at the end as you won’t pay as much interest as a 30-year mortgage for example.

It’s important to decide how long you want to repay your mortgage as well. For example, if you retire in 20 years and want to be mortgage free by then, you could choose a 20-year term if you can afford it.