How Much Can I Borrow for a Buy-to-Let Mortgage?
2026-08-15
Buy-to-let mortgage borrowing works differently from residential. With a residential mortgage, the lender asks "can you afford the payments from your salary?" With BTL, they ask "can the rent cover the payments — with a safety margin?"
This fundamental difference means some investors can borrow much more than they expect, while others get less than they need. Understanding the calculation means you can find properties that fit, identify lenders that work for you, and avoid wasting time on deals that won't get approved.
The Core Calculation: Rental Coverage
Most BTL lenders use this formula:
Minimum Rent Required = Mortgage Payment x Coverage Ratio
Where:
- Mortgage payment is calculated at the stressed rate (not your actual rate)
- Coverage ratio is typically 125% or 145%
The Stressed Rate
Lenders don't assess affordability at the rate you'll actually pay. They stress-test at a higher rate to ensure the deal survives if rates rise. Common stressed rates:
| Lender Type | Stressed Rate | Notes |
|---|---|---|
| Standard (basic rate taxpayer) | 5.5% | Most common |
| Higher-rate taxpayer (personal name) | 5.5% with 145% coverage | Tighter than basic rate |
| Limited company | 5.5% with 125% coverage | Easier affordability |
| Some specialist lenders | Pay rate (actual rate) | Rare, usually higher rates |
The Coverage Ratio
| Taxpayer Status / Structure | Typical Coverage Required |
|---|---|
| Basic-rate taxpayer (personal) | 125% |
| Higher-rate taxpayer (personal) | 145% |
| Limited company (SPV) | 125% |
The difference between 125% and 145% coverage is significant. On the same rent, the 145% requirement reduces your maximum borrowing by approximately 14%.
Worked Example: Maximum Borrowing
Property rents for £950/month. How much can you borrow?
Scenario A: Basic-rate taxpayer, 125% coverage, 5.5% stressed rate
Required rent = Monthly interest x 1.25 £950 = Monthly interest x 1.25 Monthly interest = £760 Annual interest at 5.5% = £9,120 Maximum loan = £9,120 / 0.055 = £165,800
Scenario B: Higher-rate taxpayer, 145% coverage, 5.5% stressed rate
£950 = Monthly interest x 1.45 Monthly interest = £655 Annual interest at 5.5% = £7,862 Maximum loan = £7,862 / 0.055 = £142,900
Scenario C: Limited company, 125% coverage, 5.5% stressed rate
Same as Scenario A: £165,800
:::stats £165,800 | Max Loan (Basic Rate / Company, £950 rent) £142,900 | Max Loan (Higher Rate, Personal, £950 rent) £22,900 | Difference (14% less for higher-rate) :::
Quick Reference Table
Maximum borrowing at 75% LTV, 5.5% stress, by monthly rent:
| Monthly Rent | Max Loan (125%) | Max Loan (145%) | Max Property (75% LTV, 125%) |
|---|---|---|---|
| £600 | £104,700 | £90,300 | £139,600 |
| £700 | £122,200 | £105,400 | £162,900 |
| £800 | £139,600 | £120,400 | £186,100 |
| £900 | £157,100 | £135,500 | £209,400 |
| £1,000 | £174,500 | £150,500 | £232,700 |
| £1,200 | £209,500 | £180,700 | £279,300 |
| £1,500 | £261,800 | £225,800 | £349,100 |
Use the Mortgage Calculator to run exact numbers for your specific rent and rate scenario.
:::tool mortgage-calculator Calculate Your Maximum Borrowing :::
What Limits Your Borrowing
1. The Rent Isn't High Enough
The most common limitation. If the property's achievable rent doesn't support the loan amount you need at the stressed rate, the lender won't approve the full amount.
Solutions:
- Buy a cheaper property (lower loan needed)
- Find a property with higher rent potential (better area, bigger property)
- Add value first to increase rent (BRRR approach)
- Increase your deposit (lower LTV = lower loan needed)
2. Personal Income Too Low
Most BTL lenders require minimum personal income of £25,000-£30,000 per year from employment, pension, or other sources. This is a hard floor regardless of how strong the rental income is.
Solutions:
- Some specialist lenders accept £15,000-£20,000 minimum
- Portfolio income (from existing properties) is accepted by some lenders
- A guarantor can help in some cases
3. Credit Issues
Adverse credit (missed payments, defaults, CCJs) limits your lender options and may reduce maximum LTV.
Solutions:
- Specialist adverse credit lenders exist (higher rates)
- Time heals — most adverse drops off credit files after 6 years
- Dispute incorrect entries with credit agencies
4. Portfolio Landlord Restrictions
At 4+ mortgaged properties, many lenders assess the whole portfolio not just the new property. If your existing portfolio has tight margins or stressed properties, it can limit further borrowing.
Solutions:
- Use lenders that don't cross-assess (some specialist lenders)
- Improve portfolio margins before applying (increase rents, remortgage to better rates)
- See Portfolio Landlord Mortgages
5. LTV Restrictions
Standard: 75% LTV. This means you need 25% deposit regardless of how much rent supports. Even if the rent could service a larger loan, lenders cap at 75% (or 80% with specialist products).
How to Borrow More
Use a Company Structure
Limited companies benefit from 125% coverage (vs 145% for higher-rate personal). This alone increases maximum borrowing by ~14% on the same rent.
Find Lenders Assessing at Pay Rate
Some specialist lenders assess at the actual rate you'll pay (e.g., 5.0%) rather than a stressed rate (5.5%). This increases maximum borrowing by ~10%. The trade-off: these products usually carry a higher rate or fee.
Increase the Rent Before Applying
If your property's rent is below market rate, increase it before applying for a mortgage. Lenders use the lower of actual rent and surveyor's rental estimate. If your rent is already at market, the surveyor will confirm it. If it's below market, you're leaving borrowing capacity on the table.
Use a Broker
Brokers know which lenders are most generous on:
- Stressed rates (some use 4.5% or even pay rate)
- Coverage ratios (some use 120% for companies)
- Rental assessment (some accept projected rent, not just current)
- Income requirements (some have no minimum income)
A good broker can increase your effective borrowing by 10-20% compared to applying directly to a high-street lender.
Top-Slice with Personal Income
Some lenders offer "top-slicing" — where they use your personal income to cover any shortfall between the rent and the required coverage. If the rent covers 120% but the lender needs 125%, they'll check whether your salary can absorb the 5% gap. This opens up properties that would otherwise fail strict rental coverage tests.
The Borrowing vs Affordability Distinction
Borrowing = how much the lender will advance (based on rent, LTV, and coverage).
Affordability = whether you can actually sustain the investment (cashflow, reserves, stress tolerance).
A lender might approve £165,000 based on rent. But if that creates a property with £30/month cashflow that goes negative on a rate rise, it's not affordable for YOU — even if it's affordable by the lender's definition.
Always run the full deal analysis after confirming borrowing capacity. Borrowing approval is necessary but not sufficient — the deal still needs to stack up.
:::tool deal-analyser Check If Your Deal Actually Works :::
Summary
- BTL borrowing is based on rent, not salary (but minimum income of £25,000 usually required)
- Coverage ratio: 125% for basic rate / company, 145% for higher rate personal
- Stressed rate: typically 5.5% (not your actual rate)
- Maximum loan on £950/month rent: £143,000-£166,000 depending on structure
- Companies can borrow ~14% more than higher-rate personal buyers on the same rent
- Increase achievable rent before applying (market rate maximises borrowing)
- Use a broker to find the most generous lender for your situation
- Borrowing approval doesn't mean the deal works — always stress-test independently
This guide is for educational purposes only. Lending criteria vary between lenders and change frequently. Always consult a qualified mortgage broker for advice specific to your situation.