The 30-second answer.
An Agreement in Principle — sometimes called a Decision in Principle (DIP) or Mortgage in Principle (MIP) — is a soft, conditional statement from a lender saying: based on what you've told us, we would in principle be willing to lend you up to £X.
It's not a mortgage offer. It's not legally binding. But it's the bit of paper estate agents and sellers expect to see before they take your offer on a property seriously.
What it actually proves.
- That a lender has done basic checks on your income and credit
They've taken a snapshot, applied their affordability rules, and confirmed they'd be willing to look further. That's enough for a seller to know you're not making up your budget.
- That you've got a realistic borrowing ceiling
Until you've got an AIP, your idea of "what we can afford" is a guess. The AIP turns it into a number you can put on an offer letter without flinching.
- That you're a serious buyer
Most estate agents in 2026 won't progress an offer without seeing one. Many won't even let you view a property without it. It's the cost of admission.
What it doesn't prove.
- It's not a mortgage offer
A full application — with documents, employer references, and a property valuation — comes later. An AIP can still turn into a decline if something on your full application doesn't add up.
- It doesn't guarantee a particular rate
Rates move. The AIP gets you in the door; the rate gets fixed when your full application is submitted.
- It doesn't tie you to that lender
You can have an AIP with one lender and apply for the actual mortgage with another. We routinely do this when a different lender becomes a better fit once the offer is accepted.
The credit-search question.
Some lenders run a soft search for the AIP — invisible to other lenders, no impact on your credit file. Others run a hard search — visible to everyone who looks at your file, and one of several factors that can nudge your credit score down a few points (temporarily).
For a single AIP this rarely matters. But if you apply for three or four AIPs in quick succession with hard-searching lenders, your file starts looking like someone shopping desperately for credit — which can hurt your eventual full application.
The question to ask before any AIP is run.
"Will this be a soft search or a hard search?" Ask before they pull anything. A good adviser will tell you up front. If you're shopping around, prefer soft-search lenders for the AIP stage — save the hard search for the lender you actually intend to apply with.
How long does it last?
Most AIPs last 60 to 90 days — long enough to find a property and get an offer accepted, not so long that the lender's assumptions about you go stale. If house-hunting takes longer (and it often does), the AIP can usually be renewed; we'd just re-run the figures to make sure nothing material has changed.
What you'll need to provide.
- Personal details
Names, dates of birth, addresses (three years of address history is standard).
- Income basics
Employer name, gross annual salary, length of employment. For self-employed applicants, latest year(s) of profits or salary-plus-dividends.
- Existing financial commitments
Loans, credit cards, car finance, child maintenance. The lender uses these to gauge your affordability headroom.
- Deposit information
How much, where it's coming from (savings, sale of existing property, gift from family).
No payslips, bank statements, or property details are needed at this stage. Those come later, at the full application.
A common misunderstanding.
People sometimes think the AIP figure is "what I can afford full stop." It isn't. An AIP figure is what one particular lender will offer, on a snapshot, against their particular affordability model. Two different lenders can produce AIP figures that vary by tens of thousands for exactly the same applicant. Picking the right lender for your circumstances is exactly the value a broker adds.
The short version.
Get an AIP before you start viewing.
You'll need one. Better to have it ready than to scramble after an offer.
Ask whether the search is soft or hard.
For the shopping-around stage, prefer soft.
Know what it does and doesn't prove.
It opens doors with sellers. It doesn't guarantee the final offer.
Your home may be repossessed if you do not keep up repayments on your mortgage. This guide is general information, not personal mortgage advice. For advice on your specific situation, book a free chat.