Put the same lump sum to work across very different homes - a leveraged buy-to-let, a Stocks & Shares ISA, an unwrapped index fund, a cash ISA, savings and bonds - and see the after-tax outcome and annualised return side by side. The UK tax treatment that makes or breaks each option is built in.
What you’re investing
£
£
yrs
Expected returns (%/yr)
%
%
%
%
%
Buy-to-let assumptions
%
%
%
%
%
Best after-tax outcome
Stocks & Shares ISA
£100,483 after 10 years
Investment
Final value
Return p.a.
Stocks & Shares ISA
£100,483
7.2%
Buy-to-let (leveraged)
£90,995
3.6%
Index fund (unwrapped)
£85,804
5.5%
Cash ISA
£74,542
4.1%
Fixed-rate bond
£68,298
3.2%
Cash savings
£65,893
2.8%
Buy-to-let here: £64,000 cash in (deposit + £11,500 SDLT surcharge + fees) buys a £200,000 property. Year-one net cash flow -£1,200; CGT on sale £15,788. Leverage amplifies the capital-growth assumption — try changing it.
Compared on after-tax final value and annualised return on the cash invested. ISAs are tax-free; savings/bonds are taxed above the Personal Savings Allowance; unwrapped funds bear dividend tax plus CGT on exit. Assumptions are yours to change — returns aren’t guaranteed and property is illiquid.
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Why comparing like-for-like is hard (and why tax is the key)
The honest answer to property or stocks depends entirely on assumptions and tax wrappers. This tool makes those explicit. Liquid investments compound on the cash you put in; buy-to-let uses your cash as a deposit and borrows the rest, so a modest rise in the property's value is magnified across the whole asset - but mortgage interest, Section 24 tax, running costs and Capital Gains Tax on exit all bite. Change the assumptions and the winner changes, which is exactly the point.
Cash ISA & Stocks & Shares ISA - growth is completely tax-free.
Cash savings & fixed-rate bonds - interest taxed at your marginal rate above the Personal Savings Allowance (1,000 basic / 500 higher).
Index fund (unwrapped/GIA) - dividends taxed each year (2026/27 dividend rates 10.75%/35.75%/39.35% above the 500 allowance) and Capital Gains Tax (18%/24%) on the gain when you sell.
Buy-to-let - leveraged: the model includes the 5% SDLT surcharge, interest-only mortgage cost, Section 24 tax on rent, and CGT on the gain at sale.
Worked example
50,000 over 10 years, higher-rate taxpayer.
Stocks & Shares ISA at 7%: grows to about 100,000 entirely tax-free.
Buy-to-let: 50k deposit buys a roughly 200k property (25% down). With 3% capital growth, 6% gross yield and Section 24, year-one cash flow is slightly negative but leverage on the capital growth still builds equity - final net worth depends heavily on the growth and yield you assume.
The comparison flips toward property at higher capital-growth or yield assumptions, and toward the ISA at lower ones - try your own figures.
Looking ahead: from April 2027 savings income will be taxed at 22%/42%/47% and property income will get its own 22%/42%/47% rates, both 2 percentage points higher than today. That will make the tax-free ISA wrappers and the leverage maths even more important to model carefully.
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Frequently asked questions
Is this a recommendation to choose one investment?
No. It is an illustration based on the assumptions you enter. Returns are not guaranteed, property is illiquid and concentrated, and your tax position and goals matter enormously. This is general information, not financial advice.
Why does buy-to-let sometimes lose to a simple ISA here?
Leverage cuts both ways. With modest capital growth, the mortgage interest, Section 24 tax (for higher-rate landlords) and CGT on exit can outweigh the benefit of borrowing - while a Stocks & Shares ISA compounds completely tax-free. Raise the growth or yield assumption and property can pull ahead. Seeing that trade-off clearly is the whole point.
How is buy-to-let made comparable to the liquid options?
Your cash is treated as the deposit plus buying costs (SDLT surcharge and fees). The model accumulates net rental cash flow after Section 24, grows the property value, then sells at the end netting off the remaining mortgage and CGT. Everything is compared on annualised return (CAGR) on the total cash invested.
Report a bug or ask a question about this calculator
Important: BrickCrunch provides general information and estimates only — this is not financial, tax, mortgage or legal advice. Calculations are simplified and your circumstances may differ. UK tax and rate figures are checked against gov.uk (21 June 2026 (2026/27 tax year)) but rates change and errors are possible. Always confirm figures with gov.uk or a qualified professional before making decisions.
