A Mortgage in Principle (also called an Agreement in Principle or Decision in Principle — all the same thing) is a lender's estimate of what they'd likely lend you, based on a preliminary check. It's usually valid for 30–90 days depending on the lender, so the right time to get one is right as you start seriously viewing properties — not months before, and not after you've already found a home.
What a Mortgage in Principle actually is
A Mortgage in Principle, Agreement in Principle, and Decision in Principle are three names for the same document — different lenders simply use different terminology. It's a written estimate of how much a specific lender would likely be willing to lend you, based on a preliminary review of your income, outgoings and, usually, your credit file.
It's genuinely useful — it gives estate agents and sellers a real signal that you're a credible buyer, and it gives you a realistic budget before you start viewing. But it is explicitly not a mortgage offer. The lender hasn't verified your documents, hasn't valued a specific property, and hasn't done full underwriting. It can still say no at full application, even after issuing a Mortgage in Principle, if something in the detail doesn't match what was assumed.
Soft search vs hard search — this genuinely varies
Some lenders issue a Mortgage in Principle using only a soft credit check, which doesn't affect your credit score and isn't visible to other lenders. Others use a hard search, which is recorded on your file and can be seen by future lenders — several hard searches in a short window can have a small negative effect on your score.
Whether a specific lender uses a soft or hard search isn't standardised, and it isn't always obvious from their website. If you're planning to shop around for a Mortgage in Principle from more than one lender, ask directly which type of check they use first — it's a genuinely easy question to ask, and it avoids an avoidable dent to your file right before you need your credit looking its best.
Why timing matters more than people expect
Because a Mortgage in Principle expires — typically after 30 to 90 days depending on the lender — getting one too early is a common, easily avoidable mistake. If you secure one three months before you're realistically ready to make an offer, it may have already lapsed by the time you actually need it, meaning you're renewing it (and potentially triggering another credit check) right when you should be focused on the property itself.
The better sequence is: get your finances in order first, understand roughly what you can afford, then get your Mortgage in Principle right as you begin actively viewing properties — so it's still valid when you find the right one and need to move quickly on an offer.
What you'll typically need
- Proof of income (payslips, or accounts/SA302s if self-employed).
- Details of your regular outgoings and any existing credit commitments.
- An estimate of your deposit and the property price range you're considering.
- Basic personal details — most straightforward cases return a result in 10–15 minutes online.
What happens after
Once you have an accepted offer on a property, a Mortgage in Principle becomes the starting point for your full mortgage application — the same lender (or a different one, if you choose to shop around) will then verify everything properly: full documentation, a formal credit check if one hasn't already been done, and a valuation of the actual property. Only after all of that does a lender issue a formal mortgage offer, which is the document that's actually binding.