Investment Calculator
Adjust the inputs below. Results update as you type.
How it works
Investment growth calculators answer a planning question: if contributions and a constant return assumption hold, what might the balance look like later? Numbarn’s tool supports forward growth and “solve for contribution” style goals so you can work from a target as well as from a starting habit.
Enter a starting balance, recurring contribution, expected annual return, and time horizon. Compounding frequency changes results slightly; contribution timing (beginning vs end of period) also matters over long horizons. Treat the rate as a planning assumption, not a promise—historical averages hide sequence-of-returns risk, fees, and taxes.
A practical workflow is to run three cases: conservative, baseline, and optimistic returns, then ask whether the contribution level still fits your budget in the conservative case. If you are solving for the deposit needed to hit a goal, compare that required contribution against paycheck and emergency-fund constraints before increasing market risk. Fees and account type (taxable vs tax-advantaged) are not fully modeled here; pair this page with retirement and tax tools when those details drive the decision.
Input guidance
- Starting balance should exclude money you still need as an emergency fund.
- Contribution amount should be what you can sustain after taxes and living costs.
- Expected return is a planning assumption—run a conservative case too.
The formula
FV = P·(1+r)^n + PMT·(((1+r)^n − 1)/r) projects a lump sum plus regular contributions, where r is the periodic rate of return and n the number of periods.
Worked example
Invest $10,000 up front plus $300/month at 8% for 20 years: the balance grows to about $223,000, with roughly $82,000 contributed and $141,000 from compound growth.
More examples to test
- $10,000 start + $400/month for 20 years at 5% vs 7%: compare ending balances.
- Solve for the monthly contribution needed to reach $500,000 in 18 years from $25,000.
How to interpret results
Use the projection to set contribution habits and goal feasibility. Prefer the conservative case when the decision is irreversible spending today.
When this can be inaccurate
Fees, taxes, sequence-of-returns risk, and irregular contributions are simplified or omitted.
Change history
- July 2026: Expanded solve-for-contribution planning notes and scenario workflow.
- June 2026: Growth engine and modes reviewed for publication.
Site-wide corrections also appear on the corrections log.
Frequently asked questions
Are returns guaranteed?+
No. Market returns vary year to year and can be negative. This is a projection based on a constant assumed rate, useful for planning, not a promise.
How do fees affect results?+
Fees compound against you. A 1% annual fee can cut a long-term balance by tens of percent, so low-cost index funds often win over decades.
What about taxes?+
Taxes on dividends, interest, and gains reduce real returns in taxable accounts. Tax-advantaged accounts like IRAs and 401(k)s shelter growth.
Should I use a single return rate?+
No. Run at least a conservative and baseline return so the plan still works if markets underperform your hope case.
Does this include fees and taxes?+
Usually only as simplified assumptions. Lower your return input to approximate fees, and compare taxable vs tax-advantaged accounts separately.
Guided next steps
Want the full workflow? Use this calculator inside a step-by-step guide.
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