What is a Mortgage Agreement in Principle (AIP)?

Key takeaways

• A mortgage agreement in principle provides an estimate of how much a lender is willing to lend you.
• Most AIPs are valid for 30 to 90 days and can usually be renewed if your finances remain stable.
• Requesting a soft credit check is essential to protect your credit score during the early stages.
• Having an AIP makes you a more attractive buyer to estate agents and sellers.
• An AIP is not a guarantee of a mortgage and is subject to full application checks and property valuations.

What is an agreement in principle for a mortgage?

A mortgage agreement in principle is an official statement from a lender indicating how much they are prepared to lend you. It is based on a basic check of your finances and acts as a preliminary green light for your search.

Often referred to as a mortgage agreement in principle (AIP) or decision in principle (DIP), this document is your financial foundation. It is often the first milestone mentioned in our first-time buyer home buying guide because it transforms you from a casual browser into a qualified buyer. While it is not a legally binding contract, it serves as an indication of intent from a bank or building society and provides you with a realistic price range for your property search.

How does an agreement in principle work?

Lenders review your basic financial information to calculate your borrowing limit. This process provides a reliable estimate for your property search without requiring a full, formal mortgage application or a specific property address.

The process is usually straightforward and can often be completed online or via a mortgage broker. The lender looks at your salary and regular outgoings to ensure you can afford the monthly repayments. By establishing this limit early, you can account for the hidden costs of buying a house such as legal fees and moving expenses, ensuring your total budget remains sustainable.

What information do lenders need for a mortgage agreement in principle?

You will typically need to provide proof of income, details of your monthly outgoings, existing debt obligations, and your address history. Lenders use this data to assess your affordability and creditworthiness.

Lenders will ask for your annual salary, any bonuses or overtime pay, and a breakdown of your monthly spending, including credit card balances and student loan payments. You do not usually need to provide physical documents, such as payslips, at the agreement-in-principle stage, but the information you provide must be accurate. If you eventually move to a full application and the numbers do not match your evidence, the lender may withdraw their support.

How long does a mortgage agreement in principle last?

Most agreements in principle remain valid for between 30 and 90 days. If you do not find a property within this timeframe, you can usually renew it, though your financial circumstances must remain the same.

The expiration date exists because lenders frequently update their interest rates and lending criteria. Your own financial situation might also change, such as a new job or a change in monthly outgoings. If your mortgage in principle expires, you will need to ask the lender to refresh it. This usually involves a quick review of your recent payslips or bank statements to ensure nothing significant has shifted.

If you are house hunting in a fast-moving market, keeping your MIP up to date is essential. Sellers are often hesitant to accept offers from buyers whose documentation has expired.

Pro tip: If your decision-in-principle is nearing its expiry date and you are about to make an offer, contact your lender or broker immediately. Having a fresh document ready can be the difference between a seller choosing you or another buyer.

Does an agreement in principle affect my credit score?

Most lenders use a soft credit check to provide an agreement in principle, which does not affect your credit score. However, some still use hard searches, so you must confirm this before you apply.

A soft credit check is like a background look at your credit report that other lenders cannot see. It does not leave a mark on your file. In contrast, a hard search is a deep dive that stays on your record for 12 months. Too many hard searches in a short window can make you look desperate for credit, which might lower your score.

Always ask the lender or your mortgage adviser which type of search they perform. Protecting your credit score at this stage is vital because you will need a healthy file when you eventually submit your full mortgage application. Read our credit scores for house hunters to help you get mortgage ready. We also offer guidance on how to improve your credit score and what you need to know about your credit report.

Why is an agreement in principle important when buying a home?

An agreement in principle proves to estate agents and sellers that you are a qualified buyer who has already started the financial process. It gives them confidence that you are serious about your move, which means less risk of a deal falling through or being gazumped.

In the UK property market, estate agents often ask to see a mortgage in principle before they even allow you to view a property. This is especially common for high-demand homes. It filters out "window shoppers" and ensures that only serious contenders are entering the property.

Beyond showing you are serious, it gives you a clear boundary for negotiations. Knowing your upper limit means you can bid with confidence. It also speeds up the process once your offer is accepted, as the lender already has your basic details on file.

Pro tip: Always have a digital or printed copy of your AIP ready when attending viewings. Being able to show an agent your proof of funds on the spot can help you secure a second viewing or get your offer to the seller faster.

What is the difference between an agreement in principle and a mortgage offer?

An agreement in principle is an estimate of borrowing potential, while a mortgage offer is a formal, legally binding contract. The offer is made only after a full application and a satisfactory property valuation.

The agreement in principle is the "maybe" stage, while the mortgage offer is the "yes" stage. To move from an agreement in principle to a formal offer, the lender will conduct a thorough audit of your finances. They will also require a mortgage valuation to ensure the property is worth the price you are paying.

It is important to remember that a lender can still decline your full application even if they gave you a mortgage in principle. This might happen if they find issues during a deep dive into your credit history, or if the property itself has structural problems that make it poor collateral for the loan.

What happens after you get a mortgage in principle?

Once you have your mortgage-in-principle document, you can confidently view properties and make offers. While you wait for an offer to be accepted, start assembling your team of professionals, including conveyancers, surveyors and removal experts — find and compare quotes for trusted home-moving services.

You will need a solicitor or licensed conveyancer to handle the legal transfer of the property. Understanding how long conveyancing takes can help you manage your expectations during this phase and clarify what fees you’ll be expected to pay, ensuring there are no surprises.

Pro tip: When choosing your legal representative, consider these 10 questions to ask a conveyancing solicitor to ensure they are the right fit.

You should also consider which type of survey you need. A mortgage valuation is for the lender's benefit only, but a RICS home survey protects you by identifying hidden defects. Finally, check the latest stamp duty guide to calculate your tax obligations.

Finally, do not leave your removals planning until the last minute. Booking a firm early in the process not only helps you budget for the move but also secures your preferred date. Find out how to get accurate removal quotes and find a local removal company with Moving Compared.

Common reasons a mortgage is declined after an agreement in principle

A mortgage can be declined if a full credit check reveals new issues, your financial circumstances change, or the property valuation is lower than expected. Lenders may also find discrepancies in your documentation.

A decision in principle is a preliminary approval, not a guarantee. If you take out a new car loan or miss a credit card payment after getting your agreement in principle, the lender may decide you can no longer afford the mortgage. Similarly, if the property you want to buy has structural issues or is significantly undervalued relative to the purchase price, the lender might refuse to lend the full amount. This is why it is essential to maintain a stable financial profile until the keys are in your hand.

Conclusion

Getting an agreement in principle is a great start, but the work does not stop there. To keep your move on track, you should:

• Find a solicitor to start the legal paperwork. You can read our guide to conveyancing to understand what’s involved.
• Decide on a survey level. Our survey vs mortgage valuation guide explains why the lender's check is not enough.
• Get a clear idea of total costs. Check our house survey costs article to help with your overall budget.

Moving Compared is here to simplify these steps. Our tools help you find the best rates on the core services that make a house a home.