What Is a Mortgage in Principle and How Long Does It Last in the UK?
What a Mortgage in Principle Actually Is
A mortgage in principle (MIP) — also called an agreement in principle (AIP) or decision in principle (DIP) — is a written statement from a lender saying they’d be willing to lend you a certain amount, based on a quick assessment of your finances. It is not a formal mortgage offer, and it doesn’t guarantee you’ll get the money. Think of it as a lender saying, “Based on what you’ve told us, we’re interested.”
Estate agents ask for one before they’ll take you seriously as a buyer. Sellers want proof you can actually afford their property. A mortgage in principle gives you that proof — quickly, and usually for free.
What Information Do You Need to Get One?
Lenders will ask for the basics:
- Your name, address, and date of birth
- Your income (salary, self-employed earnings, benefits, rental income)
- Your outgoings and existing debts
- The size of your deposit
- The property value you’re targeting
Most lenders run either a soft credit check (which doesn’t affect your credit score) or a hard credit check (which does leave a mark) at this stage. Always ask which type they use before applying. If you’re shopping around, multiple hard searches in a short window can dent your credit score — so this matters.
Tip: Use a whole-of-market mortgage broker to get an MIP. They’ll know which lenders use soft checks and which products you’re most likely to qualify for, saving you time and protecting your credit file.
How Long Does a Mortgage in Principle Last?
Most mortgage in principles are valid for 60 to 90 days. Some lenders offer a shorter window of 30 days; a handful will stretch to 6 months. After it expires, you simply apply for a new one — it’s not a lengthy process.
Here’s a rough breakdown by lender type:
| Lender Type | Typical Validity |
|---|---|
| High street banks | 60–90 days |
| Building societies | 60–90 days |
| Specialist lenders | 30–60 days |
If you’re still house hunting when yours expires, renew it. Don’t assume it rolls over automatically — it won’t.
Does It Guarantee You’ll Get a Mortgage?
No. This is the most important thing to understand. A mortgage in principle is based on self-reported information and a limited credit check. The full mortgage application involves:
- Verification of your income (payslips, SA302s for the self-employed, bank statements)
- A full hard credit search
- A property valuation by the lender
- Affordability stress testing
If anything changes between your MIP and your full application — you lose your job, take on new debt, or the property valuation comes in low — the lender can decline you. It happens. Don’t overstretch your budget just because you’ve got a figure on paper.
Why You Still Need One Before You Start Viewing
Estate agents in the UK routinely ask for a mortgage in principle before arranging viewings — particularly in competitive markets like London, Manchester, or Edinburgh. Some will refuse to book viewings without one. Sellers, understandably, don’t want their property taken off the market by a buyer who hasn’t checked they can actually borrow the money.
Beyond the practicalities, getting an MIP forces you to think clearly about your budget before you fall in love with a property you can’t afford. If you’re buying with a partner, it also confirms your combined borrowing power early on.
How Much Can You Borrow?
Most lenders will offer between 4x and 4.5x your annual income. Some will go to 5x or even 5.5x for higher earners or certain professions (doctors and solicitors, for example, sometimes qualify for enhanced income multiples).
Example: If you earn £45,000 a year, you might be offered between £180,000 and £202,500 at 4–4.5x. With a 10% deposit of £22,500, that puts you in the market for properties up to around £225,000.
Remember: what a lender will offer and what you should borrow aren’t always the same thing. Factor in stamp duty, solicitor fees, surveys, and ongoing costs like council tax and service charges (if buying a flat) before committing.
Useful Resources
- MoneyHelper (moneyhelper.org.uk) — free, impartial guidance on mortgages and home buying, backed by the government
- FCA Register — check any broker or lender is authorised at register.fca.org.uk before you hand over personal information
- Shared Ownership and First Homes — if you’re a first-time buyer struggling to hit the deposit threshold, check eligibility for government-backed schemes via the Own Your Home website
Common Mistakes to Avoid
- Applying to multiple lenders using hard searches — this can damage your credit score before your full application. Use a broker or stick to soft-search tools first.
- Treating the MIP figure as your budget ceiling — always account for purchase costs on top of the property price.
- Letting it expire without renewing — if you’re still searching after 90 days, get a fresh one. An expired MIP carries no weight with estate agents.
- Changing jobs or taking on new debt after getting your MIP — lenders re-check your finances during the full application. Any changes can affect the outcome.
The Bottom Line
A mortgage in principle takes 15–30 minutes to obtain, costs nothing, and is a near-essential step in the UK home-buying process. It’s valid for 60–90 days in most cases, gives estate agents the confidence to take you seriously, and helps you set a realistic budget before you start viewing. Just don’t mistake it for a mortgage offer — the real work comes later.
Get one, use it wisely, and don’t let it lull you into a false sense of security.
This article is for informational purposes only and does not constitute regulated financial advice. Mortgage products and eligibility criteria change regularly. Always seek advice from a qualified, FCA-authorised mortgage adviser before making any financial decisions.