The mortgage in principle: what it is, what it isn't

5 min read · June 2026

An estate agent asks if you have a mortgage in principle. You say yes — or hastily apply for one the evening before a viewing. Either way, there's often a vague understanding of what it actually is. Here's the clear version.

What a mortgage in principle actually is

A mortgage in principle (also called an Agreement in Principle, AIP, or Decision in Principle, DIP) is a conditional statement from a lender saying they would, in principle, be willing to lend you a certain amount — subject to a full application and full underwriting.

It is not a mortgage offer. It is not a guarantee. It can be withdrawn, reduced, or qualified at any point during a full application. Getting an AIP tells you approximately how much a lender thinks you could borrow based on limited information — it doesn't mean you'll definitely get that mortgage.

Soft check vs hard check — this matters

When you apply for an AIP, the lender runs a credit check. This will be either:

• A soft check: visible only to you on your credit file, not to other lenders. This does not affect your credit score. Apply for as many soft-check AIPs as you like to compare lenders.
• A hard check: visible to all lenders who check your credit file. Multiple hard checks in a short period can negatively affect your credit score and may make other lenders more cautious.

Always ask whether an AIP involves a soft or hard check before you apply. Many online AIP tools from brokers use soft checks. Some direct lender applications use hard checks. The lender should tell you which upfront.

How long it lasts

AIPs typically last 60–90 days, depending on the lender. If yours expires before you find a property, you can renew it — usually with another credit check (ask whether soft or hard again).

Note that if your circumstances change between getting the AIP and making a full application — new debt, change in employment, reduced income — the AIP becomes less reliable as a guide to what you'll actually be offered.

Why estate agents want it

Estate agents ask for an AIP to filter out buyers who are unlikely to be able to complete. It's not a legal requirement to have one before viewing or offering, but in a competitive market, vendors and their agents want confidence that you're a credible buyer.

Having an AIP also helps you. It means you know roughly what you can borrow before you fall in love with a house that's out of reach. It sharpens your search and prevents a lot of disappointment.

The gap between AIP and approval

The real work happens in the full mortgage application: income verification, bank statements, payslips, existing debt checks, valuation of the property. An AIP is based on what you tell the lender; a mortgage offer is based on what you can prove.

Common reasons an AIP doesn't convert to a full offer: income that doesn't match what was declared, unresolved credit issues, property the lender won't lend on, or changes in financial circumstances. None of these are the end of the world — but they're worth knowing about as early as possible.