What Is an Interest-Only Mortgage and Should You Get One?

An interest-only mortgage is exactly what it sounds like: every month you pay only the interest on the loan. The capital balance — the amount you originally borrowed — never reduces. At the end of the term you owe the lender the original loan in full, and you have to repay it from somewhere.

For residential buyers, interest-only is now rare and tightly regulated. For buy-to-let landlords, it's the default product.

How interest-only works

You borrow £200,000 over 25 years at 5% interest.

• Repayment mortgage: monthly payment £1,169 (capital + interest). At end of 25 years, you owe £0.
• Interest-only mortgage: monthly payment £833 (interest only). At end of 25 years, you still owe £200,000.

The lower monthly payment is the appeal. The £200,000 due at the end is the catch.

What you do at the end

You must repay the original loan. Three common ways:

1. Sell the property and pay off the mortgage from the proceeds (BTL landlords typically plan this)
2. Sell other investments (ISA, SIPP, investment portfolio) you've been building specifically for this purpose
3. Inheritance or other lump sum that's been agreed with the lender

If you can't repay, the lender will work with you — but ultimately may force a sale.

Why residential interest-only is rare today

After the 2008 crash, regulators tightened interest-only rules dramatically. Today, most UK lenders won't offer residential interest-only mortgages without:

• A clearly defined and credible repayment vehicle (not "I'll downsize", which lenders accept reluctantly)
• A high deposit (often 25–40% LTV)
• Strong income (£75k+ for many lenders)
• Some lenders also require evidence of investment progress every few years

Even when offered, the rates are usually 0.1–0.3% higher than equivalent repayment products.

Why BTL is still mostly interest-only

For BTL landlords, interest-only makes sense:

• Maximises monthly cash flow from rental income
• Mortgage interest is the main allowable expense (with tax credit at 20%)
• Plan is to sell the property at the end of the term and repay the loan
• Capital growth (if any) is the landlord's profit on top

Read Buy-to-let mortgages for beginners.

Repayment vs interest-only — direct comparison

A £200,000 loan over 25 years at 5%:

Interest-only costs ~£100,000 more in interest over 25 years (because the capital balance never reduces, the interest base stays high).

But: you have £336/month more cash flow during those 25 years (£100,800 over 25 years), which you can invest.

If you invest £336/month at 6% real returns over 25 years, you'd have ~£230,000. That's £30k more than the £200,000 you'd owe — a small win.

If you invest at 4% real returns: ~£170,000. £30k short — a small loss.

The interest-only "investment plan" therefore depends on disciplined investing at returns higher than your mortgage rate. Most people don't do this consistently.

Full comparison: Repayment vs interest-only mortgage.

Part-and-part mortgages

Some lenders offer part-and-part — a hybrid where some of the loan is repayment and some is interest-only. This combines the cash flow advantage of interest-only with partial capital reduction.

Useful for borrowers who can't afford full repayment but want to chip away at the balance.

Who residential interest-only is right for

Genuinely suitable for:

• High earners with lumpy income (e.g. partners in law/finance) who plan to use bonuses for capital reduction
• Investors with substantial taxable portfolios who can offset gains efficiently against the mortgage payoff
• Older borrowers with definitive downsizing plans (Retirement Interest-Only mortgages — see RIO mortgages)
• Property developers doing short-term refurbishments before sale (often actually using bridging loans — Bridging vs mortgages)

Generally unsuitable for:

• First-time buyers
• Anyone without a credible repayment plan
• Anyone whose plan is "I'll figure it out in 25 years"

Switching from interest-only to repayment

You can usually switch at any time, either with your existing lender (a product transfer) or by remortgaging. The monthly payment will rise — sometimes substantially — but you start paying down the loan.

For borrowers worried about the end-of-term liability, switching part-way through the term is a sensible move. Sooner is better — the longer you wait, the higher the eventual repayment portion needs to be.

Read Repayment vs interest-only.

The "interest-only legacy" problem

Many people who took out interest-only mortgages in the 2000s have reached or are approaching the end of their term with no clear repayment plan. The FCA and lenders have strict guidance on managing this:

• Lenders typically write to borrowers 10, 7, 5, 3 and 1 years before maturity
• Options include extending the term, switching to repayment, or selling the property
• Equity release (lifetime mortgage) is sometimes used by older borrowers — see Lifetime mortgage and equity release

If you have an interest-only mortgage and no plan, engage with your lender now. They have legal duties to help.

Common interest-only mistakes

• Treating interest-only as a permanent solution — it's a deferral
• Relying on house price growth to repay the loan
• Plan = "I'll downsize" — lenders increasingly reject this as too vague
• Not investing the cash flow advantage — you save monthly but spend it on lifestyle
• Forgetting the FCA reviews — engage with letters from your lender

Get a free mortgage quote — a broker can model interest-only vs repayment for your situation.

Frequently asked questions

Can I get a residential interest-only mortgage as a first-time buyer? Almost never — most lenders require strong existing wealth and a clear repayment vehicle. FTBs are pushed toward repayment.

Can I overpay an interest-only mortgage? Yes — overpayments reduce the capital balance and lower future interest. Most lenders allow 10% per year penalty-free.

Do interest-only mortgages have higher rates? Slightly higher — 0.1–0.3% premium typical for residential. BTL interest-only rates are essentially the standard BTL rate.

Can I switch back from repayment to interest-only? Possible but requires a new application. You'll need to demonstrate a credible repayment vehicle.

What if I can't repay at the end? Speak to the lender 5+ years before maturity. Options include term extension, switch to repayment, sale of property, equity release.

Is interest-only the same as a tracker mortgage? No — repayment basis (interest-only vs repayment) and rate type (fixed vs tracker) are independent choices. You can have any combination.

This article is for informational purposes only and does not constitute financial advice. Always consult a qualified mortgage adviser before making a decision.