Figures are illustrative only, ignore charges and tax, and are not a forecast or personal recommendation.
This calculator projects the future value of a monthly investment plan — no lump sum required, just a regular contribution, an assumed annual return, and a time horizon. It's built for the most common way many people actually invest: setting up a standing order into an ISA or SIPP each month and letting it run.
Why regular investing is popular
Investing a fixed amount every month, regardless of whether markets are up or down, is sometimes called pound-cost averaging. It removes the pressure of trying to time a single lump-sum entry point, spreads purchases across many different price levels over time, and — perhaps most importantly — fits naturally around a monthly income, making it easier to sustain for years or decades. Our guide on regular monthly investing versus a lump sum covers the evidence and trade-offs between the two approaches in more depth.
How the projection works
The calculator compounds your monthly contribution at the annual rate you enter, divided across twelve months, assuming each contribution is invested at the start of its month and grows from that point onward. It reports the projected future value, the total amount you'll actually have contributed, and the growth on top — the same underlying calculation used in our Compound Interest Calculator, isolated here to just the monthly-contribution component.
Worked example
£200 invested every month for 20 years at an assumed 6% annual return produces a total contribution of £48,000, but — because of compounding — a projected value well above that figure. Extending the same plan by just 5 more years (to 25) increases the projected value by considerably more than 25% extra, because the earliest contributions have had the most time to compound. This is the core argument for starting a regular investment plan as early as possible, even with modest amounts.
What if I have both a monthly amount and a starting lump sum?
Use our combined Investment Growth Calculator instead, which accepts both an initial investment and a monthly contribution together. Alternatively, if you want to directly compare investing a lump sum immediately against spreading the same total out via monthly contributions instead, our Lump Sum vs Regular Investment Calculator runs that comparison for you.
Frequently asked questions
Does this account for ISA or pension tax relief?
No — this is a pure growth projection. If your monthly contribution goes into a SIPP, remember that pension contributions typically receive tax relief added on top of what you pay in, which this calculator does not add automatically; enter your gross (post-relief) contribution amount if you want to reflect that.
What return rate should I assume for a monthly investment plan?
This depends heavily on what you're invested in — a global equity tracker, a cautious multi-asset fund, and a bond fund have very different long-run return expectations and risk levels. Match the assumption to your actual portfolio rather than a generic figure.
Can I increase my monthly contribution part-way through?
The calculator assumes a flat monthly amount for the whole term. To model a step up in contributions, run the projection separately for each period at the relevant contribution level and combine the results.
Is investing monthly better than saving up and investing annually?
Evidence is mixed and depends on market conditions during the specific period — investing as soon as money is available (whether monthly or in a lump sum) has historically outperformed delaying to save up a bigger sum, simply because money spends more time invested and compounding.
How does this compare to a Regular Investment discount on my platform?
Separately from investment growth, some platforms offer lower dealing charges for regular monthly investment instruments compared with one-off trades, which can make monthly investing cheaper as well as more disciplined — worth checking with your specific provider.
Common mistakes when planning regular investments
One common mistake is setting a monthly contribution that feels comfortable when first set up but isn't reviewed as income changes, meaning the plan quietly falls behind what could realistically be afforded and invested as earnings grow. Treating the contribution amount as something to revisit at least annually — alongside pay rises or changes in expenses — tends to produce noticeably better long-term outcomes than a "set and forget" amount chosen once and never revisited upward.
A second mistake is stopping contributions during a market downturn out of caution, when in fact continuing to invest the same amount through a falling market means buying at lower prices — one of the practical benefits of pound-cost averaging described earlier. Pausing contributions specifically because markets have fallen tends to work against the investor over the long run, compared with maintaining a steady, disciplined contribution schedule regardless of short-term market movements.
Is it better to invest weekly, monthly, or less often?
Monthly is the most common frequency because it lines up naturally with income, but the difference between weekly, monthly, or quarterly investing (of the same total amount) has only a small effect on long-run outcomes compared with the much larger effect of simply investing consistently and for longer.
What happens if I miss a month's contribution?
Missing an occasional contribution won't meaningfully change a multi-decade projection — the bigger risk is missing many months in a row or stopping altogether, which removes both the missed contributions and all the growth they would have gone on to generate.
Does the platform I use for regular investing matter?
Yes — some platforms charge lower dealing fees, or none at all, specifically for regular monthly investment instructions compared with one-off trades, and ongoing platform charges vary too, both of which affect your real-world outcome beyond what this growth-only projection shows.
What if I want to invest a variable amount depending on what I can afford each month?
The calculator assumes a flat figure, so use a conservative, sustainable average of what you expect to invest across a typical year rather than your best-case monthly figure, to avoid an overly optimistic projection.
One more practical point: standing orders that debit your account the day after payday, rather than relying on a manual transfer, tend to produce far more consistent long-term contribution histories, since the money is committed before it has a chance to be spent on something else. This "pay yourself first" ordering is a small logistical habit with an outsized effect on whether a regular investment plan like the one modelled here actually survives contact with real life over 10, 20, or 30 years.