Contributions vs. growth over time
Green is the money you put in; blue is the market growth on top. Updates as you change the inputs.
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Investment
Investment Calculator
Project the future value of an investment from a starting amount, an expected return rate, and optional regular contributions, or flip it around to see what return rate a goal actually requires.
Projected ending value
$150,715
Starting amount$15,000
Total contributions$54,000
Total growth (interest)$81,715
Growth multiple2.18×
How it works
Every investment projection, regardless of what you're actually investing in, comes down to the same four variables interacting with each other. Change any one of them and the other three have to absorb the difference.
- Starting amount. What you're putting in on day one, savings earmarked for the goal, an inheritance, proceeds from selling something else.
- Return rate. The average annual growth you're assuming. This is the number that's hardest to know in advance and the one most worth stress-testing with a range rather than a single guess.
- Time horizon. How long the money stays invested. Longer horizons give compounding more time to work and generally smooth out short-term volatility.
- Contributions. Money added after the starting amount, typically on a monthly or annual schedule. Contributions made earlier compound for longer than contributions made later, even if the total dollar amount is identical.
This calculator can solve for the ending value given the other three inputs, or work in reverse to show the annual return rate a specific goal would require, useful for sanity-checking whether a target is realistic.
Worked example
Starting with $15,000, contributing $300 per month, at an assumed 7% annual return over 15 years:
| Item | Amount |
|---|---|
| Starting amount | $15,000 |
| Total contributions (15 years) | $54,000 |
| Total growth | $81,715 |
| Projected ending value | $150,715 |
Matching the return rate to the investment type
The right assumption for "return rate" depends heavily on what's actually being modeled, and it's worth being conservative rather than optimistic:
- Cash-equivalents, savings accounts, money market funds, short-term CDs, trade a low, fairly predictable return for very low risk of loss.
- Bonds sit between cash and stocks: higher-rated bonds pay less but are more stable, while lower-rated bonds pay more to compensate for a higher chance of default.
- Stocks and stock funds have historically offered the highest long-run average returns of the mainstream options, paired with the widest year-to-year swings, a number that looks fine averaged over 20 years can still include some brutal individual years.
- Real estate returns come from both price appreciation and, for rental property, ongoing income, which makes the "return rate" for real estate more of a blended estimate than a single published figure.
Because the true future return of any of these is unknowable in advance, it's good practice to run this calculator twice, once with a conservative rate and once with an optimistic one, to see the realistic range of outcomes rather than anchoring on a single number.
Frequently asked questions
What four numbers does an investment projection actually need?
A starting amount, an expected return rate, a time horizon, and an optional regular contribution, everything else is calculated from those.
Is a higher return rate always the better choice?
No, higher expected returns typically come with wider swings and more risk of loss, so the rate should be weighed against your time horizon and risk tolerance, not chosen in isolation.
How much does a regular contribution change the outcome versus a lump sum?
Often quite a lot over long horizons, each contribution compounds from the day it's made, so steady contributions can catch up to or beat a larger one-time deposit made later.
Why use an average annual return instead of a guaranteed one?
Most real investments don't grow at a constant rate; the average smooths out year-to-year swings for planning purposes, but actual results will vary above or below it.
Can I use this to estimate a goal instead of a forecast?
Yes. Switch the calculator to a target goal and it will estimate the annual return you would need, which is useful when comparing a realistic investing plan to your financial objective.