Monthly contribution goal calculator:
how much do you need to invest each month?
Enter your target portfolio value, starting amount, time horizon, and expected return. The calculator tells you exactly how much you need to invest each month — and how much of the final result comes from compounding rather than your own contributions.
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What this calculator shows
- The required monthly contribution to hit a target portfolio value.
- Total contributions vs estimated growth — how much compounding does the work.
- A real-target reference using your inflation assumption.
- A note if your starting amount already reaches the goal on its own.
- Taxes — no withholding, capital gains, or wealth tax modeled.
- Broker fees, FX costs, or ETF spreads.
- Inflation-adjusted contributions — the monthly amount stays constant.
- Variable or irregular contributions.
Monthly contribution needed to reach your goal
Enter your target, starting amount, horizon, and return assumption. Results update live as you type.
- Return sensitivity is high. A 1% change in your assumed return can shift the required contribution significantly. Always run the numbers at a lower return too.
- Fees are invisible here. Reduce your return input by your all-in cost estimate for a realistic net figure.
- Time is your main lever. Extending the horizon usually reduces required contributions more than optimising the return assumption.
Assumes constant monthly contributions invested at the chosen timing (start or end of month), compounded monthly. No taxes, trading fees, FX costs, or cash drag are modeled.
What is happening under the hood
Your starting amount is grown for the full horizon using standard monthly compounding. Monthly contributions are modeled as an annuity — either end-of-month (ordinary annuity) or start-of-month (annuity due), where start-of-month contributions each earn one extra month of growth. The calculator solves for the contribution that makes the combined future value equal your target.
Taxes, capital gains treatment, FX conversion costs, ETF spreads, broker commissions, and cash drag are all excluded. For a more realistic net return, reduce your expected return by an all-in cost estimate before running the calculation.
- Stress-test the return. Run the calculation at 5%, then 7%, then 4%. The spread tells you how sensitive your plan is to return assumptions.
- Extend the horizon first. Adding two or three years to your time horizon often reduces the required monthly amount more than finding a fund with a 0.1% lower TER.
- Account for costs. Deduct your estimated all-in fee drag from the return input. A gross-of-fee result flatters the plan.
- Consistency beats precision. A contribution you reliably make every month is worth far more than a theoretically optimal number you cannot sustain.
Know your monthly number. Now find a broker that will not eat it.
Fees, FX markups, and spreads quietly reduce your effective return — which means you need to contribute more each month to hit the same target. Interactive Brokers is consistently the lowest-cost option for European investors running a regular contribution plan, with no conversion markup on FX and no custody fees on most accounts.
Go deeper
Frequently asked questions
Is the monthly contribution invested immediately?
Yes. The calculator assumes each contribution is invested on schedule — at the end of the month by default. If you batch trades or regularly delay investing, the real outcome will be slightly worse. Use the Cash Drag calculator to model the cost of that delay separately.
Should I use a conservative return assumption?
Yes. Most investors overestimate long-run returns and underestimate friction. Entering a lower return increases the required monthly contribution — which is the safer planning outcome. A conservative plan you overshoot is far better than an optimistic plan that falls short.
Why does start-of-month timing change the required contribution?
Because each contribution gets one extra month of compounding compared to end-of-month deposits. That means the same monthly amount produces a slightly higher final value — so you need slightly less per month to hit the same target when you invest at the start of the month.
What does the real target figure mean?
It shows your nominal target expressed in today's purchasing power, using the inflation rate you entered. It is a reference number only. The calculator does not adjust contributions for inflation, so use the real target to sense-check whether the nominal figure is actually meaningful in real terms given your assumed inflation rate.
How do I factor in fund fees and broker costs?
Reduce the expected return by your estimated all-in annual drag: ETF TER, tracking difference, recurring broker costs, and any FX conversion markup. For example, if you expect 7% gross but estimate 0.3% per year in total costs, enter 6.7% as your return. The Broker Total Cost Calculator can help you estimate that all-in number.
QuantRoutine provides educational content only. Nothing on this page is an offer, solicitation, or recommendation to buy or sell any security or to open an account with any specific broker. Investments can lose value, and past performance does not guarantee future results. Calculator results are planning estimates only — actual outcomes depend on your real return, fees, taxes, and contribution consistency. Always verify current pricing and eligibility on the broker's official website before making decisions. You are responsible for your own investment, tax, and legal decisions.