Today's serious buyers all do this before they even book a viewing
It is not a legal requirement, and you do not technically need one to book a viewing. But a Mortgage in Principle has become the standard first step for buyers who are genuinely ready to move, and there is a straightforward reason why. According to Rightmove's research of nearly 1,000 buyers conducted in June 2025, just under three quarters of people said they wanted to know what their budget would be before they started searching for their next home. A Mortgage in Principle is how that question gets a specific, lender-verified answer.
What a Mortgage in Principle actually is
A Mortgage in Principle, also referred to as an Agreement in Principle, Decision in Principle, or Mortgage Promise depending on the lender, is a personalised statement from a mortgage lender showing how much they may be willing to lend based on the information you have provided. It is not a formal mortgage offer and it does not guarantee that a mortgage will be granted, but it reflects an initial assessment of your financial position and produces a realistic borrowing figure you can plan around.
Combined with your available deposit, it gives you a clear sense of the price range you can search within. A buyer who knows their realistic ceiling is making better use of their time at every stage of the search.
How long it takes and what it costs
Rightmove's guide notes that completing an online Mortgage in Principle application typically takes around ten minutes. Once submitted, the lender's decision is usually generated within seconds. The process is free in most cases when done online, though some brokers may charge a fee for their services, so it is worth checking in advance.
A Mortgage in Principle is typically valid for up to 90 days, though this varies by lender. If it expires before you have found a property, you will need to apply again, and the result may differ due to any changes in your circumstances or the lender's criteria.
The credit check question
Most lenders use a soft credit check when issuing a Mortgage in Principle. A soft check is not recorded on your credit file and does not affect your credit score, even if you apply to multiple lenders. Some lenders use a hard check, which does leave a footprint. Rightmove's guide advises checking which approach your chosen lender uses before applying, since multiple hard checks in a short period can have a cumulative effect on your credit score.
When you move on to a full mortgage application following an accepted offer, soft checks from the earlier stage typically convert to hard checks at that point.
Why sellers and agents value it
Having a Mortgage in Principle in place before making an offer signals to both the selling agent and the vendor that you are financially prepared and in a position to proceed. In a market where sellers are assessing not just the offer figure but the credibility and reliability of the buyer behind it, this matters. A buyer who can confirm they have a Mortgage in Principle in place, alongside the name of a broker or lender they are working with, is a more straightforward proposition to accept than one whose financial position is entirely unverified.
A single Mortgage in Principle can be used for multiple properties while it remains valid. It does not commit you to the lender who issued it. If a better product becomes available or your search takes you to a different price range, you are free to apply elsewhere.
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