Pound Cost Averaging Calculator United Kingdom

Should you invest a windfall straight away or feed it in month by month? Pound cost averaging is the second approach: spreading a fixed sum over regular instalments. This calculator grows a lump sum from day one and compares it with the same total drip-fed in equal monthly amounts, both at one return you choose, so the only difference between the two answers is timing.

How pound cost averaging works

Instead of deciding that today is the day to invest everything, you invest the same amount on a fixed schedule whatever the market is doing. When prices are low your money buys more units, and when they are high it buys fewer, so over time your average purchase price tends to sit below the average market price and you never buy everything at the worst moment. It turns one large, nerve-wracking decision into a series of small automatic ones.

Lump sum versus drip-feeding

A lump sum is fully invested from the first day, so every pound has the most time to compound. Drip-feeding leaves part of your money uninvested for months, earning far less than you hope the market will. When markets rise, as they do more often than not, the lump sum usually finishes ahead. Drip-feeding wins only when the market falls while you are still investing, letting later instalments buy cheaply.

So the choice is between more expected growth and protection against investing everything just before a fall. Neither is always right, and the gap depends on the return you assume and how long the drip-feed runs.

A worked example

You have £12,000 and assume a 12% annual return over twelve months. Invested at once, it grows to about £13,522. Drip-fed at £1,000 a month, each instalment compounds only for the months left after it goes in, so the total reaches about £12,809. The difference, about £713, is the cost of holding money back while you spread it out. A longer drip-feed or a higher assumed return widens the gap; at a zero return it disappears, because timing makes no difference without growth.

Why the timing gap exists

In the lump sum, all your money earns a return for the whole period. In the drip-feed, the first instalment earns a return for nearly the whole time but the last earns almost nothing, so on average the money is invested for only about half the period. The calculator treats each instalment as invested at the start of its month, the standard way to model regular contributions at the beginning of each period.

Assumptions and limitations

This is an illustration, not a forecast. It uses one constant return for every month of both scenarios, which no real market delivers; real returns are volatile, and that volatility is what occasionally gives drip-feeding its advantage. It ignores dealing charges, platform fees, taxes and any interest the waiting cash might earn, and assumes you stay invested and keep to the schedule. Because the return is your input rather than a guaranteed rate, use the output to understand the timing effect and test scenarios, not to predict what your investments will be worth.

About This Pound Cost Averaging Calculator

Use this pound cost averaging calculator to get an instant estimate based on the figures you enter. Adjust the inputs above to match your situation, or browse all our calculators to plan your next step.