Common Mistakes to Avoid
The most costly investing mistakes UK investors make — from timing the market and home bias to letting fees erode returns and panicking during downturns.
Common Mistakes to Avoid
Even well-intentioned investors can sabotage their own returns. Research from Dalbar consistently shows that the average investor underperforms the market by 3–4 % per year — not because they pick bad investments, but because of behavioural mistakes. Here are the most common ones.
1. Trying to Time the Market
"I will wait until the market drops before I invest." This sounds logical but is nearly impossible in practice. Missing just the 10 best days in the FTSE All-Share over a 20-year period can halve your total return.
| Scenario (£10,000 invested, 20 years) | Final Value |
|---|---|
| Stayed fully invested | £36,800 |
| Missed the 10 best days | £18,300 |
| Missed the 20 best days | £11,400 |
Illustrative example based on historical FTSE All-Share data. Past performance does not guarantee future results.
The best days often occur during the worst periods — right after a crash, when most people are too scared to be in the market. Time in the market beats timing the market.
2. Home Bias
UK investors disproportionately overweight UK stocks. The UK represents approximately 4 % of global stock market capitalisation, yet many UK portfolios hold 30–50 % in UK equities.
This creates concentration risk: heavy exposure to a small number of sectors that dominate the UK market (financials, energy, mining, consumer staples). A global tracker gives you the UK and the other 96 % of the world's opportunities.
3. Ignoring Fees
As we covered in Module 2, fees compound relentlessly. A fund charging 1.5 % versus 0.15 % can cost tens of thousands of pounds over a 30-year investment horizon. Always check the OCF (Ongoing Charges Figure) before investing, and compare platform fees too.
Common hidden costs:
- Dealing charges — some platforms charge £5–12 per trade
- Exit fees — check before transferring to a new provider
- FX charges — buying non-GBP funds may incur 0.5–1.5 % conversion fees
- Platform percentage fees — can become expensive as your portfolio grows
4. Not Using Your ISA Allowance
The £20,000 ISA allowance resets every 6 April and cannot be carried forward. Any investment growth inside an ISA is completely free of income tax, capital gains tax, and dividend tax — forever.
Yet many UK investors hold investments in a taxable GIA when they have unused ISA allowance. If you can afford to invest, the ISA should almost always be the first port of call.
5. Panic Selling During Downturns
Markets fall. It is normal and expected. The FTSE 100 has experienced drawdowns of −20 % or more roughly once every 5–7 years. The crucial point: every single one has been followed by a recovery to new highs.
Selling during a downturn locks in your losses and means you miss the recovery. A study by Fidelity found that their best-performing accounts belonged to investors who had forgotten they had accounts — doing nothing was the winning strategy.
6. Concentration Risk
Putting a large percentage of your portfolio into a single stock, sector, or asset class means one bad outcome can devastate your wealth. Even excellent companies can collapse — think of Carillion (2018) or Thomas Cook (2019), where UK shareholders lost everything.
Rules of thumb:
- No single stock should exceed 5 % of your portfolio
- No single sector should exceed 25 % of your equity allocation
- Be especially wary of holding your employer's shares — your income and your investments should not depend on the same company
7. Performance Chasing
Buying last year's best-performing fund is one of the most reliable ways to underperform. The asset class or fund that tops the league tables one year often reverts to the mean the next.
The Periodic Table of Returns shows that asset class rankings shuffle almost randomly from year to year. The only consistent winner? A diversified portfolio that includes many of them.
8. Not Having a Plan
Investing without a clear goal (retirement at 60, house deposit in 5 years, children's university fund) leads to ad-hoc decisions and emotional reactions. Write down:
- What you are investing for
- When you will need the money
- How much risk you can tolerate
- How much you will invest each month
Then automate it. Review annually. Resist the urge to tinker.
This module is educational and does not constitute financial advice. Your circumstances are unique — consider speaking with a regulated financial adviser for personal guidance.
Explain Like I'm 5
The biggest mistake is getting scared and pulling your money out when things look bad -- like running away from a rollercoaster just before it goes back up. Also, do not put all your sweets in one bag in case you lose it. Have a simple plan, keep adding a little every month, do not peek too often, and let your money grow quietly like a plant in the garden.
Key Takeaways
- Time in the market beats timing the market — missing just the 10 best days over 20 years can halve your total returns.
- UK home bias means many investors overweight a market that is only 4 % of the global total — diversify globally.
- Always use your £20,000 ISA allowance before investing in a taxable GIA — the tax savings compound enormously.
- Panic selling during downturns locks in losses and means missing the recovery; every major market drawdown has eventually recovered.
- Have a written investment plan with clear goals, timeline, and contribution amount — then automate it and review annually.
Build your investment plan and track progress automatically.
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