Pound Cost Averaging (DCA) Simulator
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Simulate monthly DCA investing with realistic price volatility. See your average cost per share, total shares acquired, and gain or loss at each stage of your investment.
When you invest a fixed amount monthly, you buy different numbers of shares each month depending on the price. The harmonic mean of the prices you pay is always equal to or lower than the arithmetic average price — this is the mathematical advantage of DCA.
| Month | Price | £200 invested | Shares bought | Cumulative shares |
|---|---|---|---|---|
| Month 1 | £10.00 | £200 | 20.00 | 20.00 |
| Month 2 | £8.00 | £200 | 25.00 | 45.00 |
| Month 3 | £12.00 | £200 | 16.67 | 61.67 |
| Totals | Avg £10.00 | £600 | 61.67 shares | DCA avg: £9.73 |
The arithmetic average price was £10.00, but your DCA average cost is only £9.73 (£600 ÷ 61.67 shares) — saving £0.27 per share.
Pound cost averaging (PCA) means investing a fixed amount — say £200/month — at regular intervals regardless of the current market price. When prices are high, your £200 buys fewer units or shares. When prices are low, it buys more. Over time this produces an average cost per unit that is lower than the arithmetic average of prices you invested at. For example: invest £100 at £10/share (10 shares) and £100 at £5/share (20 shares) — you own 30 shares for £200, averaging £6.67/share, even though the average price was £7.50. This is the mathematical advantage of PCA.
A good UK DCA strategy: (1) Choose a low-cost global index fund — Vanguard FTSE All-World, iShares MSCI World, or similar, with an ongoing charge below 0.25%. (2) Invest monthly via a Stocks & Shares ISA (tax-free growth and withdrawals). (3) Set an automatic direct debit on payday before you can spend it. (4) Never skip months — consistency matters more than timing. (5) Do not stop during market downturns — dips are when DCA is most powerful, buying more units cheaply. (6) Review and increase your monthly amount as your income grows. (7) Stay invested for at least 10 years for DCA to show its full benefit.
For most UK investors building wealth from monthly income, DCA is the only practical strategy — you invest what you earn each month. The academic debate between DCA and lump sum applies primarily when you have a large lump sum (inheritance, bonus, property sale proceeds) and must decide whether to invest it all immediately or spread it over months. In that case, lump sum beats DCA about 67% of the time historically (Vanguard research). However, if DCA helps you stay invested through volatile markets without panic-selling, the psychological benefit can outweigh the expected statistical disadvantage compared to lump sum.
Yes — you can invest into a Stocks & Shares ISA every month, which is the most tax-efficient way to DCA in the UK. The annual ISA allowance is £20,000 (2025/26 tax year), equivalent to £1,667/month. All growth and withdrawals are completely tax-free — no capital gains tax, no income tax on dividends. Most major UK ISA providers (Vanguard, Hargreaves Lansdown, Fidelity, iWeb, AJ Bell) support monthly direct debits into your chosen funds. You can pause, increase, or decrease contributions at any time without penalty. The ISA allowance resets on 6 April each year.
DCA actually works best in falling markets. When prices decline, your fixed monthly investment buys more units at lower prices. If prices later recover, those cheaply-bought units contribute disproportionately to your gains. This is why long-term investors should not stop DCA during market downturns — the months when it feels worst (market falling) are often when DCA provides the greatest long-term benefit. The danger is stopping contributions during a crash and missing the recovery. Historical data shows that markets have always eventually recovered from corrections; the question is always when, not if (for broad diversified indices).