Buy-to-let vs index fund
Bricks you can stand in, or a passive fund you never think about. Both build wealth over decades, but they ask completely different things of you — and the tax rules have tilted noticeably against property in recent years.
The verdict
There’s no single winner — they’re different investments for different temperaments. Buy-to-let offers control, the power of leverage and a tangible asset, but comes with real work, heavy tax and concentration risk. An index fund offers true passivity, instant diversification, low cost and the shelter of an ISA, but no leverage and no control. If you want a hands-off investment, the fund usually wins on simplicity; if you want to actively build a property business and use a mortgage to amplify returns, buy-to-let can still pay — if the numbers stack up after tax.
Buy-to-let
A rental property you own and manage
- Leverage — a mortgage amplifies gains
- Monthly rental income
- A tangible asset you control
- 5% stamp duty surcharge to buy in
- Mortgage interest only a 20% tax credit
- Real work: tenants, repairs, voids, admin
Index fund
A passive fund tracking a whole market
- Completely passive — no management
- Instant diversification, low cost
- Tax-free inside an ISA
- No leverage to amplify returns
- Values fall as well as rise
- No tangible asset or rental income
The tax stack has turned against property
A decade ago buy-to-let was a far easier win. Three changes have since reshaped the maths, and any honest comparison has to start there. First, the stamp duty surcharge on additional properties rose to 5% — on a £250,000 buy-to-let that’s around £15,000 before you’ve collected a penny of rent. Second, Section 24 ended full mortgage interest relief: landlords now get only a 20% tax credit instead of deducting interest, which hits higher-rate taxpayers hard on leveraged properties. Third, while the capital gains tax rate on residential property was trimmed to 18% basic and 24% higher, the annual tax-free allowance has shrunk to just £3,000.
None of that makes buy-to-let a bad investment — but it does mean the headline yield rarely survives contact with reality. A property advertised at a 6% gross yield often nets just 2–3% once mortgage interest, letting fees, insurance, maintenance and void periods are paid. The quirk worth knowing: that’s the figure to judge it on, not the gross. If the deal only works on the assumption of house price growth, it’s a bet, not an investment.
Two very different shapes of investment
Strip away the tax detail and the real difference is what each demands of you. An index fund is something you can genuinely forget: you pay in, it tracks a whole market, costs are tiny, and inside a Stocks and Shares ISA the growth and income are free of tax. There are no tenants, no 2am calls about a boiler, no licensing rules to track. The trade-off is that you can’t borrow to amplify it, and you have to sit through the market falling without panicking.
Buy-to-let is the opposite bargain. It’s a part-time business as much as an investment — but it offers something the fund can’t: leverage. Put down a 25% deposit and you control 100% of an asset, so if property rises, your return is calculated on the whole value, not just your stake. That amplification is buy-to-let’s genuine edge. The price is the work, the tax, the illiquidity, and the concentration of a large sum in one property in one town.
| Factor | Buy-to-let | Index fund |
|---|---|---|
| Effort | Active — ongoing management | Passive — none |
| Leverage | Yes (mortgage) | No |
| Diversification | One property | Whole market |
| Liquidity | Low — months to sell | High — days |
| Tax shelter | None (ISA can’t hold it) | ISA / SIPP |
| Entry cost | High (deposit + 5% SDLT) | Low |
When each one wins
Buy-to-let wins when…
- You want to use leverage to amplify returns.
- You’ll treat it as a business and do the work (or pay someone).
- You can find strong net yields, often outside the South East.
- You value a tangible asset and direct control.
The index fund wins when…
- You want a genuinely hands-off investment.
- You value diversification over a single concentrated bet.
- You want to shelter growth tax-free in an ISA.
- You might need access to your money at short notice.
It’s worth saying these aren’t mutually exclusive. Plenty of investors hold both — an index fund as the passive core, a buy-to-let as an active, leveraged satellite. The right answer depends less on which produces a higher number on a spreadsheet and more on whether you actually want to be a landlord. If the honest answer is no, the fund’s simplicity is worth a great deal.
Common questions
Is buy-to-let or an index fund a better investment?
Neither is universally better — they suit different investors. Buy-to-let offers leverage, rental income and control, but demands active management and faces heavy tax. An index fund is passive, diversified, low-cost and can grow tax-free in an ISA, but offers no leverage. The right choice depends on whether you want a hands-off investment or are willing to run what is effectively a property business.
What return does buy-to-let actually give after costs?
A property with a headline gross yield of around 6% often nets just 2–3% once mortgage interest, letting fees, insurance, maintenance and void periods are accounted for. Capital growth can add to that, but it’s unpredictable. The net yield, not the gross, is the figure to judge a deal on — if it only works assuming house prices rise, it carries significant risk.
How have tax changes affected buy-to-let?
Three changes have squeezed returns: a 5% stamp duty surcharge on additional properties, the Section 24 rules replacing full mortgage interest relief with a 20% tax credit, and a capital gains tax allowance cut to £3,000 (with property gains taxed at 18% or 24%). Together these make buy-to-let more expensive to enter, hold and exit than it was a decade ago.
What’s the advantage of leverage in buy-to-let?
With a mortgage, a deposit of around 25% lets you control 100% of a property’s value. If the property rises, your gain is calculated on the whole value, not just your deposit — amplifying your return. This leverage is buy-to-let’s genuine edge over an index fund, where you invest only your own cash. Leverage also amplifies losses if values fall.
Can I hold an index fund in an ISA but not a property?
Correct. Index funds can be held inside a Stocks and Shares ISA, where growth and income are entirely free of UK tax, up to your annual ISA allowance. A buy-to-let property cannot be sheltered this way, so its rental income and capital gains are taxable. This tax shelter is a meaningful long-term advantage for the fund.
Can I invest in both?
Yes, and many investors do. A common approach is an index fund as a passive, diversified core, with a buy-to-let as an active, leveraged satellite for those who want property exposure and are happy to do the work. They’re not mutually exclusive, and combining them can balance the fund’s simplicity with property’s leverage and income.
Related tools & guides
How we put this together
Comparison reflects current UK rules for buy-to-let: a 5% stamp duty surcharge on additional properties, Section 24 mortgage interest relief as a 20% tax credit, and capital gains tax on residential property at 18% (basic) or 24% (higher) with a £3,000 annual allowance. Net rental yields of 2–3% against ~6% gross reflect typical published figures.
The index fund is treated as a passive, diversified, low-cost market tracker, holdable tax-free within a Stocks and Shares ISA. Returns for both are illustrative; property and equity values can fall as well as rise, and individual outcomes vary widely by location, deal and market.
We review this comparison when property tax rules or ISA allowances change.