Mortgage in principle (AIP) explained
A plain-English guide to the UK Mortgage Agreement in Principle. What it is, why every serious first-time buyer needs one before offering, how to get one, how long it lasts, and what happens at the full application stage.
- Know what the AIP is and isn't
- Understand when and how to get one
- Avoid the common AIP mistakes
Built for UK first-time buyers. The AIP is preliminary — speak to an FCA-authorised broker for advice on your specific case.
Quick answer
A Mortgage Agreement in Principle (AIP)is a lender’s preliminary statement of how much they’d be willing to lend you. It usually comes from a soft credit search, takes hours to days, costs nothing, and lasts 30–90 days. It’s not a binding mortgage offer — that comes later — but it’s the document UK estate agents expect to see with a serious offer on a property.
Get one before you start viewing seriously. Without it, your offers are weaker and the timeline after offer-accepted is longer.
Why an AIP matters before offering
Four real-world reasons UK first-time buyers should get an AIP before they start putting offers in.
- Agents expect to see one with serious offers
Most UK estate agents now ask first-time buyers for an AIP before they'll formally put an offer to the seller. Showing up without one signals you're not yet ready to proceed, which means weaker negotiating position and offers more likely to be brushed aside.
- It tells you what's realistic
The AIP is the first concrete confirmation of how much a lender will actually lend you, based on your real income, outgoings and credit profile — not the slightly optimistic online calculator. It's the moment your budget becomes a real number rather than a guess.
- It surfaces problems early
If a lender's underwriting flags issues — an unrecognised credit search, an unsettled default, a high credit-card balance — the AIP process is where you find out. Far better to fix these before you've offered on a property than to discover them at the full application stage.
- It shortens the post-offer timeline
An AIP already in hand means the full mortgage application can start within days of offer accepted. Without one, you're scrambling to apply while the rest of the chain ticks impatiently.
How to get a mortgage in principle
Three routes, with different trade-offs.
Direct from a lender
Apply online with a bank or building society. Usually free, often instant decision. Limitation: the AIP is only with that one lender, on that one lender's criteria. If they decline, you start over.
Through a mortgage broker
A broker takes your details once and applies to the lender most likely to accept your specific profile. Often faster overall (you don't waste time on a likely decline), and the broker can pivot if needed.
Through a comparison site
Some comparison sites offer an AIP via a tied broker. Convenient, but the tied broker has access to a limited lender panel — fine for clean cases, weaker for anything non-standard.
For most UK first-time buyers, the broker route gives you the widest view of the market and the best chance of avoiding a wasted application. See do I need a mortgage broker? for the decision criteria.
What lenders check at the AIP stage
AIPs are quick because most of the checks are automated against high-level details. Here’s what gets reviewed.
- Income
Salary (and how stable it is), bonuses, commissions, regular overtime, second income, self-employment profit. Lenders apply income multiples — typically 4–4.75x annual income, sometimes 5x or more for higher earners.
- Outgoings
Credit commitments (loans, credit cards, car finance), regular monthly bills, childcare, and household costs. Affordability stress-tests typically model your monthly payment at 1–3% above the actual rate.
- Deposit and source of funds
How much you're putting in and where it's from. Gifted deposits, family loans, sale of assets and savings each get treated slightly differently. Larger deposits usually unlock better rates and wider lender choice.
- Credit profile (soft search)
Lenders do a SOFT search at AIP stage — visible to you on your credit file but not affecting your credit score. They're looking for missed payments, defaults, recent applications and how much of your credit limit you're using.
- Property
AIPs are usually issued without a specific property in mind, but the lender's criteria implicitly assume a standard freehold or leasehold property. Non-standard construction (concrete prefab, ex-council, above shop, listed) can trigger criteria checks the AIP wouldn't normally flag.
AIP vs full mortgage application
The AIP is the start of the process. The full application, after your offer is accepted, is the formal commitment from the lender.
| AIP | Full application | |
|---|---|---|
| Cost | Free (usually) | Lender / arrangement / valuation fees often £200-£1,500+ |
| Time | Same day to 2-3 days | 1-2 weeks of paperwork + 2-4 weeks underwriting |
| Credit impact | Soft search only — no impact on credit score | Hard search — recorded on credit file, may dip score slightly |
| Binding? | Indicative only — not a guarantee | Formal mortgage offer issued at the end |
| Duration | Usually 30, 60, or 90 days | Mortgage offer typically valid 3-6 months |
Common AIP mistakes
Five things UK first-time buyers most often get wrong.
- Treating the AIP as a guarantee
It isn't. AIPs are based on the data you provided and an automated assessment. Full underwriting at application stage can change the outcome — particularly if the property valuation, income paperwork or credit search throws up something unexpected.
- Applying to multiple lenders simultaneously
Two or three hard searches in a short window can look risky to lenders and dip your credit score. Use the soft-search AIP route to compare, then commit to one full application.
- Not refreshing an expired AIP
AIPs typically last 30–90 days. If your search runs longer, the AIP expires and you'll need a fresh one. Agents won't accept an expired AIP with an offer.
- Major spending or borrowing between AIP and offer
A new car loan, big credit card purchase, or job change between AIP and full application can change the outcome materially. Keep your finances steady through the search and offer process.
- Maxing out the AIP figure on offer
Just because the AIP says you can borrow £250,000 doesn't mean you should. Lender stress-tests are different from real-life comfort. Pressure-test your monthly payment at the offer price before committing.
Ready for your AIP?
Get introduced to a mortgage broker
HomeReady can introduce you to a whole-of-market FCA-authorised broker who can produce an AIP fast — usually within a few days of the first conversation. They’ll explain fees and options upfront before any commitment.
Mortgage in principle FAQs
Quick answers to the questions UK first-time buyers most often ask about AIPs.
What is a mortgage in principle (AIP)?+
A Mortgage Agreement in Principle (sometimes called a Decision in Principle or DIP) is a lender's preliminary statement of how much they'd be willing to lend you, based on the income, outgoings and credit-check details you provide. It's not a binding mortgage offer — that comes later at full application — but it's strong enough that UK estate agents now expect to see one when you make a serious offer on a property.
How long does a mortgage in principle last?+
Usually 30, 60, or 90 days depending on the lender. If you haven't had an offer accepted by then, the AIP expires and you'll need to apply for a fresh one. Refreshing a recent AIP with the same lender is usually quick and doesn't trigger a new credit search if it's within a short window.
Does a mortgage in principle affect my credit score?+
Usually no. Most UK lenders use a SOFT search at AIP stage, which is visible only to you on your credit file and doesn't affect your score. A HARD search happens at the full mortgage application stage. Always confirm with the lender or broker before they pull your file — some smaller lenders do still hard-search at AIP.
How long does it take to get a mortgage in principle?+
With most major UK lenders: same day for a clean PAYE application, sometimes within minutes. More complex cases (self-employed, contractor, gifted deposit, recent credit issues) can take 1–3 working days as the underwriter reviews. Through a broker, the initial fact-find usually adds a day or two on top.
Is a mortgage in principle a guarantee I'll get the mortgage?+
No. The AIP is based on the high-level data you provided and an automated check. Full underwriting at the formal application stage involves payslip evidence, bank statements, property valuation, and a hard credit search — any of which can change the picture. Most AIPs do convert to full mortgage offers, but a meaningful minority don't.
Can I get a mortgage in principle without a specific property?+
Yes — this is the normal way. The AIP confirms how much the lender would lend you against a standard property. The specific property gets factored in at the full application stage, when the lender's surveyor or AVM (automated valuation model) values it. Some unusual properties may not qualify even with an AIP in hand.
Should I get more than one mortgage in principle?+
Sometimes — but be careful. Multiple soft searches don't hurt your credit. Multiple hard searches in a short window can. If you want to compare lenders, get AIPs through the same broker (who applies once and submits to multiple lenders behind the scenes if needed), or stick to soft-search AIPs only. Don't run two full applications simultaneously.
What documents do I need for an AIP?+
For an initial soft-search AIP, usually none — you self-declare income and outgoings. For an AIP with a manual review or going through a broker, you'll typically need recent payslips (last 3 months), bank statements (last 3 months), proof of ID, proof of address, and details of any deposit source. Having these ready speeds everything up.
Related guides
Other guides that pair well with the AIP stage.
Do I need a mortgage broker?
Whether to get your AIP via a broker or direct from a lender — the trade-offs explained.
Before speaking to a mortgage broker
Get your numbers, documents and credit picture in order so the AIP conversation is quick and useful.
How to make an offer on a house
What to do with the AIP once you have it — including how to mention it to estate agents for maximum effect.
First-time buyer guide UK
The complete journey — where the AIP fits among the rest of the steps.
Once you have the AIP
Know your numbers before you offer
The AIP tells you what a lender will lend. The affordability check tells you what's comfortable to actually live with each month.
Ready to go beyond this tool?
The Buyer Planner pulls your deposit, borrowing, timeline, and next steps into one plan.