Mortgage in principle: what it is and why agents want one

A mortgage in principle, often shortened to AIP, is an early sign from a lender of how much you may be able to borrow. It can help you move faster when you start viewing homes, but it is not the same as a formal mortgage offer. Below: what an AIP is, whether it is usually free, what kind of credit search it involves, and why estate agents often ask to see one. Mortgages are regulated by the Financial Conduct Authority; this guide is general information, not financial advice.

Definition of Mortgage in Principle

A mortgage in principle, also called an agreement in principle or decision in principle, is a lender’s written sign of how much it would lend you based on an initial check of your finances. It is not a mortgage offer. Before making a formal offer, the lender still carries out a full affordability assessment and valuation, and the formal offer is the stage described here as legally binding on the lender.

Soft vs Hard Credit Searches

The material provided says an AIP usually involves a soft credit search that does not affect your credit score. However, there are no verified facts here about hard credit searches in this context, so no comparison can be made from the supplied evidence alone.

Duration of a Mortgage in Principle

An AIP is time-limited: the lender sets the validity period, and the expiry date is stated on the AIP itself. Validity is set by each lender, so the only number that matters is the one on your own document. If it lapses before you complete, get a fresh one: the check is quick, and a renewed AIP does exactly the same job with an updated date.

Importance of Mortgage in Principle for Agents

The material says estate agents and sellers normally expect buyers to have an AIP before accepting an offer, because it shows the buyer can realistically afford the property. In practice, that makes it useful proof at the offer stage, even though it is still only an initial indication rather than a full mortgage offer.

Key facts

Source: HM Land Registry - buying your first home — see source

Source: FCA - mortgages consumer guidance — Guidance checked August 2026

Source: FCA - mortgages consumer guidance — Guidance checked August 2026

Source: Citizens Advice - buying a home — Guidance checked August 2026