How Much to Invest Monthly to Reach Your Goal
Work out the monthly investment needed to reach a savings target — like $1 million by age 65 — from your current savings and an expected rate of return.
What this calculator answers
Most people know roughly what they want — “a million dollars by 65,” “$100,000 for a house in ten years” — but not the one number that makes it actionable: how much to put in each month. This tool solves for exactly that. You give it the goal, how long you have, what you already have saved, and an expected return, and it works out the monthly contribution that gets you there.
Under the hood it is the mirror image of growth. The compound interest calculator starts from a contribution and tells you the ending balance; this one starts from the ending balance you want and works backwards to the contribution. Same math, run in reverse.
The two things that shrink the monthly number
Two levers do most of the work. The first is time. Because compounding accelerates with each year, a longer runway means growth covers more of your goal and you have to supply less. The difference is dramatic: reaching $1 million from zero at a 7% return takes on the order of $820 a month over 30 years, but closer to $380 a month over 40 years. Ten extra years does not cut the monthly amount by a quarter — it roughly halves it. That is why “start now” is the most valuable, and most boring, piece of financial advice.
The second lever is what you already have. Existing savings keep compounding the whole time, so they quietly reduce the contribution you need. If your current balance is large enough, the calculator will tell you that you are already on track and need to add nothing at all.
A worked example
Say you are 30, have $10,000 saved, and want $1 million by 65 — a 35-year horizon at a 7% assumed return. Enter those numbers and you will see the required monthly amount, plus how the balance builds year by year. Notice how much of the final total comes from growth rather than your own deposits: over a long horizon, compounding typically contributes far more than everything you put in. If the monthly figure looks steep, try nudging the target age up a few years and watch it fall.
Turning the estimate into a plan
Use the result as a target to build a habit around, not a precise promise. A steady automatic contribution is what makes goals like these achievable; the exact figure matters less than starting and staying consistent. If markets return less than assumed, you can contribute more, work a little longer, or adjust the goal — the calculator lets you test each of those trade-offs in seconds.
What it does not include
The plan is built on a single, steady return and uses nominal dollars — it ignores inflation, taxes, and the ups and downs of real markets. A bad run of early returns can mean you need to save more than the estimate suggests, and inflation erodes the purchasing power of a fixed goal. Treat the number as a well-reasoned starting point and, for decisions that affect your finances, talk to a qualified professional.
Frequently asked questions
How much do I need to invest monthly to reach $1 million?
It depends on your time horizon, current savings, and return. Starting from zero at a 7% return, roughly $820 a month over 30 years gets you there — but only about $380 a month if you have 40 years. Use the calculator to match your own numbers.
Why does starting earlier reduce the monthly amount so much?
A longer horizon gives compounding more time to do the work, so a larger share of your goal comes from growth rather than your own contributions. Each extra decade can roughly halve the monthly amount needed.
What return should I assume?
There is no guaranteed number. A broadly diversified stock portfolio has historically averaged around 7% per year after inflation over long periods, but returns are volatile and the future is uncertain. Try a lower rate to see a more conservative plan.
Does the result account for inflation?
No. Both the goal and the contributions are in today's nominal dollars. If your goal needs to keep its purchasing power, aim higher or plan to increase your contributions over time.