Mortgage in Principle: What It Is and How to Get One (2026)

A mortgage in principle is a written estimate from a lender showing roughly how much it might be willing to lend you to buy a home, based on a quick look at your income and finances. It is not a full mortgage offer and it does not guarantee you the money, but it is one of the first practical steps almost every buyer takes. Estate agents often ask to see one before they will take your offer seriously, so it is worth understanding exactly what it is and how to get it right.

You will see this document called by several names. They all mean the same thing.

What is a mortgage in principle?

A mortgage in principle is a statement from a bank or building society that, based on the figures you have given them, they would consider lending you up to a certain amount. Lenders and brokers use a few different labels for it, which can be confusing when you are new to buying:

• Agreement in principle (AIP) — probably the most common term.
• Decision in principle (DIP) — used by many high-street lenders.
• Mortgage promise or mortgage in principle (MIP).

Whichever name you meet, the document does the same job: it gives you, and any seller or estate agent, a credible figure for your likely borrowing power before you commit to a property. Think of it as a provisional yes, not a final one. The full, binding decision comes later when you make a formal mortgage application and the lender checks everything in detail (your payslips, bank statements, the property valuation and so on).

Why bother getting an AIP?

There are three solid reasons to get an agreement in principle early:

1. It proves you are a serious buyer. In a competitive market, sellers and agents favour buyers who can show they are likely to secure financing. An AIP is the evidence.
2. It tells you your realistic budget. Rather than guessing, you get a lender's own estimate of what you can borrow, which stops you wasting time viewing homes you cannot finance.
3. It flags problems early. If something on your credit file or your income figures is going to be an issue, it is far better to find out now than after you have had an offer accepted.

How lenders decide how much to lend

Before you request an AIP, it helps to understand the rough maths lenders use. Most UK lenders cap mortgage lending at around 4 to 4.5 times your annual income, although some will stretch to 5 or even 5.5 times for certain professionals or higher earners. They then run an affordability assessment: they look at your income after tax, your regular outgoings, existing debts (car finance, credit cards, loans) and how you would cope if interest rates rose.

Two people on the same salary can be offered very different amounts. A higher earner pushed into the 40% income-tax band, for example, keeps less of each extra pound than a basic-rate taxpayer, and lenders look at what actually lands in your account. For the 2026/27 tax year the main thresholds for England, Wales and Northern Ireland are:

Now that you understand the concept and the rough lending multiples, it is worth getting a personalised estimate. Our Mortgage Affordability Calculator gives you a realistic borrowing figure in seconds based on your income and outgoings, which is the perfect thing to check before you request a formal AIP.

If you would like a second view focused purely on borrowing capacity, the How Much Can I Borrow calculator approaches the same question from the income-multiple angle.

How to get a mortgage in principle

Getting an AIP is usually quick — often a matter of minutes online. Here is the typical process:

1. Gather your details. You will need your income, employment details, monthly outgoings, the size of your deposit and some personal information (address history, date of birth).
2. Choose a lender or broker. You can apply directly to a bank or building society, or go through a mortgage broker who can request AIPs across several lenders.
3. Submit the request. The lender runs a credit check (more on this below) and applies its affordability rules.
4. Receive your AIP. If you pass, you get a document stating the maximum they would consider lending, usually valid for a set number of days.

What you need to hand

• Proof of income figures (salary, or net profit if self-employed).
• Details of regular commitments — loans, credit cards, childcare, car finance.
• Your deposit amount and where it is coming from.
• Three years of address history.

How long does a mortgage in principle last?

A common question is “how long does a mortgage in principle last?” The honest answer is that it varies by lender, but most agreements in principle are valid for between 30 and 90 days. Many high-street lenders set it at 90 days; some are shorter at 30.

If your AIP expires before you have found a property or had an offer accepted, you can simply request a new one. Renewing is usually straightforward, though the lender may run another check, so it is sensible not to apply for one the moment you start browsing — wait until you are genuinely ready to make offers.

Does a mortgage in principle affect your credit score?

This is the question that worries people most: does a mortgage in principle affect your credit score? The reassuring answer is that it usually does not — provided the lender uses a soft credit check.

• Soft check: visible only to you, leaves no mark that other lenders can see, and does not affect your score. Most online AIPs use this.
• Hard check: recorded on your credit file and visible to other lenders. A single one rarely does much damage, but several in a short period can make you look like you are desperately seeking credit, which can lower your score.

Before you apply, ask (or check the lender's small print) whether the AIP uses a soft or hard search. Avoid requesting lots of agreements in principle from different lenders in a short space of time, as repeated hard searches can dent your score just when you most need it strong.

Worked example

Let us walk through a realistic case. Priya earns £45,000 a year and wants to buy her first flat. She has saved a £25,000 deposit.

1. Income tax check. On £45,000, Priya gets the £12,570 Personal Allowance, leaving £32,430 taxed at 20% — that is £6,486 of income tax for 2026/27. All of her income sits within the basic-rate band, so lenders see a clean, predictable take-home figure.
2. Borrowing estimate. Using a typical 4.5× income multiple, a lender might consider lending around £45,000 × 4.5 = £202,500, subject to affordability.
3. Total buying power. Add her £25,000 deposit and Priya is looking at properties up to roughly £227,500.
4. Affordability adjustment. Priya also has a £250-a-month car finance payment. The lender factors this in and trims the offer slightly, landing on an AIP of around £195,000 borrowing. With her deposit, that is a buying budget near £220,000.

Priya now has a credible figure to take to estate agents. The numbers are illustrative — every lender weighs outgoings differently — but they show how income, tax, deposit and existing debts combine to set your AIP. If Priya were buying with no deposit, she would have far fewer options; our guide to no-deposit and 100% mortgages explains what is realistically available.

Common mistakes

• Treating the AIP as a guarantee. It is not a binding offer. The lender can still decline at the full application stage if your documents do not match what you declared.
• Applying too early. Request an AIP when you are ready to make offers, not months in advance — it can expire, and unnecessary checks add up.
• Requesting too many. Multiple hard searches in a short window can lower your credit score. Use a broker if you want to compare lenders without scattering applications.
• Inflating your income. Be accurate. Overstating earnings gets you a higher AIP that collapses when the lender sees your payslips, wasting everyone's time.
• Forgetting about rates. The amount you can borrow is sensitive to interest rates. Keep an eye on the market — our overview of UK mortgage rates in 2026 sets the context.
• Taking on new credit after your AIP. Opening a new credit card or car finance deal between your AIP and the full application can change your affordability and jeopardise the offer.

For more help across the whole buying journey, browse our full library of mortgage guides.

FAQs

Is an agreement in principle the same as a decision in principle?

Yes. Agreement in principle (AIP), decision in principle (DIP), mortgage promise and mortgage in principle are all different names for the same thing — a lender's provisional estimate of how much it might lend you.

Does a mortgage in principle affect your credit score?

Usually not, because most lenders use a soft credit check that only you can see. It only affects your score if the lender runs a hard check, and even then a single one rarely matters — the risk comes from making several hard-checked applications in a short period.

How long does a mortgage in principle last?

Typically 30 to 90 days, depending on the lender. Many high-street lenders set it at 90 days. If it expires before you buy, you can request a fresh one.

Can I be refused a mortgage after getting an AIP?

Yes. An AIP is not a guarantee. The lender can still decline at the full application stage if your income, credit history or the property valuation do not support the loan, or if your circumstances change.

How much deposit do I need before getting an AIP?

Most lenders want at least a 5% to 10% deposit, though a larger deposit usually unlocks better rates. You can still request an AIP with a small deposit, but it will shape the figure the lender offers.

Sources

• MoneyHelper — Mortgage agreement in principle
• GOV.UK — Income Tax rates and Personal Allowance
• MoneyHelper — How much can you borrow for a mortgage

This guide is general information, not personal financial advice. For your own circumstances, speak to a qualified adviser.