UK Monthly Investment Planner
Model monthly stocks and shares ISA contributions, one-off lump sums and UK inflation to see what your portfolio could realistically become in pounds.
Plan your monthly investing
Invested vs value
Real: £106,927 (adj. 2.9%)Frequently asked questions
What is a SIP?+
Regular investing (often called a SIP) means paying a fixed amount each month into funds or ETFs, typically inside a stocks and shares ISA, which averages out your purchase price over time.
SIP vs lump sum: which is better?+
SIPs smooth out market volatility, while lump sums maximize time-in-market when funds are available. This calculator supports both together.
What return should I assume?+
Global equity funds have historically delivered roughly 6–9% a year over long periods before charges. UK savers should also weigh cash: Bank Rate is currently 3.75%. Future returns are never guaranteed.
Can I stop or change my SIP?+
Yes, most SIPs let you pause, increase, or stop contributions any time. Consistency, however, is the single biggest driver of wealth.
How this calculator works
Regular investing means committing a fixed amount each month rather than trying to time the market. Each contribution buys more units when prices fall and fewer when they rise, which smooths your average purchase price over time.
This planner projects the value of a monthly investment plan, splitting the result into the money you paid in and the growth generated on top, so you can see how much of the outcome comes from contributions versus returns.
Formula and methodology
FV = C × [((1 + r/12)^n − 1) ÷ (r/12)]- FV
- — future value of the plan
- C
- — monthly contribution
- r
- — expected annual return (decimal)
- n
- — total number of monthly contributions
- Convert the expected annual return into a monthly rate.
- Compound each contribution for the number of months remaining in the term.
- Sum the compounded contributions to get the projected fund value.
- Subtract total contributions from the projected value to isolate investment growth.
Worked examples
Filling an ISA monthly
- • £1,666 a month (£20,000 a year)
- • 6% expected return
- • 15 years
Roughly £484,000, of which about £184,000 is growth on £300,000 invested.
Starter plan
- • £150 a month
- • 6% expected return
- • 25 years
Roughly £104,000, from £45,000 of contributions.
Assumptions
- Contributions are constant and never missed or increased with inflation.
- Returns are earned evenly each month at the rate you enter.
- Dividends and interest are reinvested in full.
- No fund charges, platform fees or dealing costs are deducted.
- The plan is held in a tax-free wrapper such as a stocks and shares ISA.
Limitations
- Actual returns arrive unevenly; a run of poor years early on can leave you well below the projection.
- Increasing contributions with earnings, which most savers do, is not modelled.
- Currency movements affect UK investors holding global funds and are not shown separately.
- The figures are nominal unless you interpret the return as a real, after-inflation rate.
Noviqen provides general information, not personalised financial advice. See our editorial policy.
UK context
A stocks and shares ISA shelters growth and income from UK income tax and capital gains tax, within the £20,000 ISA allowance for 2026/27 across all ISA types (of which up to £4,000 can go into a Lifetime ISA).
Outside an ISA, the capital gains annual exempt amount and dividend allowance are both far smaller than a decade ago, which makes using the wrapper more valuable for regular investors.
Most UK platforms allow monthly direct debits from £25 to £50, and regular investing dealing charges are often lower than one-off trades. For comparison, Bank Rate is 3.75% and CPI inflation 2.9% as of 30 July 2026.