30-year plan
Very long horizon
Monthly: No change/mo
Ending balance: +$390,300
Horizon: +10 yrs
Investment & Compound Interest Calculator — See How Your Money Can Grow
Want to know how much your investments could grow over time? This free compound growth calculator shows how starting balance, monthly contributions, expected return, and time work together. Not sure how a mortgage fits into the picture? Compare cash flow with the mortgage payment calculator and the home affordability calculator.
Want to know how much your investments could grow over time?
Educational estimates — not financial advice. Calculations run in your browser; we don't store your inputs. How we make money · Disclaimer · Privacy
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Illustrative only — actual returns vary. Many long-term diversified portfolios use planning assumptions around 7.00%–8.00% before inflation.
20 years selected
How often returns are credited (e.g. monthly for many mutual funds, daily for some high-yield accounts).
Projected balance
$300,851
Breakdown
Total contributions$130,000
Investment growth$170,851
Growth share of ending balance
56.8%
Horizon
20 years
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Decision Workspace
What-If Panel
Top 3 ranked scenarios
Stronger outcome
+$500 / mo
High cash commitment
Monthly: +$500/mo
Ending balance: +$260,463
Horizon: Same horizon
+5 years
More time to compound
Monthly: No change/mo
Ending balance: +$161,439
Horizon: +5 yrs
Personalized Tips
✓
About 57% of your ending balance is growth on contributions—time and return assumptions drive most of the story.
✓
Adding $100/month could lift your ending balance by about $52,093 at these assumptions.
Investment & Compound Growth — How This Calculator Works
An investment calculator (often searched as a compound interest calculator) helps you translate a handful of assumptions—starting balance, ongoing contributions, expected return, and time—into a projected ending balance. It does not predict markets; it illustrates compounding math so you can compare scenarios and set savings goals.
What is an investment calculator?
In practical terms, it is a planning tool that estimates how money may grow when returns are reinvested and you keep contributing on a schedule. It is especially useful for long horizons such as retirement, college savings, or building taxable wealth after your core housing costs are under control. If you are also buying a home, pair this page with the home affordability calculator and the mortgage payment calculator so your investable cash flow matches your housing payment reality.
How this calculator works
We combine three ideas you will see in most finance textbooks:
- Present lump sum that grows each period
- Regular contributions added at the end of each month
- Nominal annual return mapped to an effective monthly rate using your selected compounding frequency
The chart and year-by-year table read from the same projection so the numbers stay consistent across the page.
Formula explanation
Many articles show the classic lump-sum compound formula FV = P (1 + r/n)^(nt). With monthly contributions, the clean closed form is less intuitive, so we project month-by-month (the same approach as leading consumer finance tools): each month, the balance grows at the effective monthly rate, then your contribution is added.
balance_m = balance_(m-1) × (1 + r_month) + contribution_monthly
Where r_month is derived from your stated annual return and compounding frequency. That keeps the tool honest when you switch between monthly, daily, or annual compounding presets.
Examples
Steady monthly investing
$300/month, 7% average annual return, 25 years, monthly compounding.
The point is not the exact dollar outcome—it is that most ending wealth often comes from time + consistency, not from picking a single hot stock.
Lump sum plus top-ups
A starting balance from a bonus or sale, plus smaller monthly deposits, is a common real-world pattern.
Use the what-if panel to see how +$100/month or +5 years shifts the curve.
Benefits of using a compound growth calculator
- Scenario planning: compare conservative vs moderate return assumptions side by side
- Contribution targeting: translate a future goal into a monthly savings idea
- Education: see why starting earlier is so powerful (all else equal)
- Context for debt decisions: compare expected investment returns with loan interest using our extra payment calculator when you are weighing paydown vs invest tradeoffs
Investment strategies this tool supports
You can model ideas like dollar-cost averaging (steady monthly buys), lump-sum investing after a windfall, or gradually increasing contributions as income rises. For retirement-specific framing, also browse our retirement calculator once you have a taxable-account projection you like.
If your timeline is shorter than five years, treat stock-like returns as uncertain; many planners dial down assumed volatility for near-term goals and favor cash or shorter-duration instruments—this tool still helps you see the sensitivity of outcomes to those choices.
Related calculators on The Goat Finance
- Mortgage payment calculator — align housing cost with savings capacity
- Refinance calculator — free up cash flow or shorten term
- Rent vs buy calculator — compare paths before locking in a payment
- Credit card payoff calculator — eliminate high-interest debt that competes with investing
Investment Calculator FAQs
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