Required Monthly Investment Calculator UK
Find the monthly investment needed to reach a financial goal in a given time at an expected return.
How it works
Compound interest earns returns on both your original money and the returns already added. Adding a regular monthly contribution accelerates growth further over time.
A = P(1 + r/n)^(nt) + contributions compounded monthly- Longer time horizons benefit most from compounding
- More frequent compounding gives slightly higher growth
- The donut shows how much of your final balance is interest vs money you put in.
Frequently asked questions
How much should I invest monthly to reach a goal?
Use PMT = FV × r / ((1 + r)^n − 1), with r the monthly return and n the months. For £50,000 in 10 years at 7%, about £289 a month.
Why is the monthly total less than the goal?
Because your contributions earn compound growth along the way, so investment returns make up the difference.
What return should I assume?
A realistic long-term return for your investments. Returns vary, so test a range rather than relying on one figure.
What is pound-cost averaging?
Investing a fixed amount regularly regardless of price, which spreads purchases over time and removes the need to time the market.
Does a longer time frame lower the monthly amount?
Yes. More months mean more compounding, so each contribution can be smaller to reach the same goal.
Can I do this tax-free?
Within a Stocks & Shares ISA, up to £20,000 a year, the growth is free of UK Income and Capital Gains Tax.
The monthly amount needed for a goal
This calculator works out how much to invest each month to reach a target by a chosen date, assuming a steady return. It uses the future-value-of-an-annuity formula, solved for the monthly payment.
The formula
The monthly contribution is PMT = FV × r / ((1 + r)^n − 1), where r is the monthly return (annual / 12) and n the number of months. It accounts for each contribution compounding from the month it is made until the goal date.
Worked example
To reach £50,000 in 10 years (120 months) at a 7% annual return, you would invest about £289 a month. Your contributions total around £34,700; the remaining ~£15,300 comes from compound growth.
Investing regularly — sometimes called pound-cost averaging — spreads your buying and harnesses compounding. A Stocks & Shares ISA shelters the growth from tax. Returns vary, so revisit the plan, and consider regulated advice for big decisions.
Results are estimates for general guidance in United Kingdom and may not reflect the latest local rates, fees or rules. Check official sources before making decisions.