Investment Calculator With Compound Interest
Estimate how an investment could grow when you combine a starting balance, regular contributions, an annual return assumption and compounding frequency.
| Year | Balance | Contributed | Growth |
|---|
When to use this investment calculator
Use this page for broad investing scenarios where contributions happen over time. If you only want to model a single deposit, use the lump sum investment calculator. If you need to hit a target, use the Monthly amount to reach a goal.
Formula logic
Where the money in a 20-year projection comes from
Using this page's inputs — $10,000 to start, $300 a month, 7% compounded monthly, 20 years — the projection ends at about $196,665. It is worth breaking that into its three sources, because they behave completely differently.
| Source | Amount | Share of final balance |
|---|---|---|
| Your starting balance | $10,000 | 5% |
| Your monthly contributions | $72,000 | 37% |
| Investment growth | $114,665 | 58% |
| Total | $196,665 | 100% |
Growth supplies about 58% of the outcome over twenty years. Extend the same plan to thirty and growth's share rises to roughly 74%. The longer the horizon, the less of the result you have to fund yourself — which is the entire reason timelines matter more than deposit sizes.
The $10,000 you begin with is 12% of everything you contribute, but it grows to $40,387 — 21% of the final balance. Every dollar of it is invested for the full twenty years, while the average monthly deposit is invested for about ten.
What this calculator deliberately does not model
- Variable returns. A constant 7% is a planning convenience. Real sequences matter enormously once you begin withdrawing, and not at all while you are only contributing.
- Rising contributions. Most people can increase deposits over a career. Modelling a flat amount understates a realistic plan, sometimes substantially.
- Fees. Subtract them from the rate to approximate the drag — a 1% charge brings this projection down to about $171,714.
- Tax. Depends on account type and country, and can be the largest single adjustment of all.
- Inflation. $196,665 in twenty years buys roughly what $120,019 buys today at 2.5%.
None of these make a projection useless. They make it a scenario rather than a forecast, which is the correct way to read any of them.
Questions about investment projections
How much will my investment be worth?
With $10,000 invested, $300 a month and a 7% return compounded monthly, about $196,665 after 20 years and $447,156 after thirty.
What return should I use for an investment calculator?
Something you would still be comfortable with in a poor decade. 7% before inflation is a common long-run equity assumption; 5% is the conservative version worth testing alongside it.
Should I include my pension or 401(k)?
Include everything genuinely invested for the same goal, including employer contributions. Employer matching is a return on your deposit before any market growth, and leaving it out understates the projection.
Why does this differ from my broker's projection?
Usually fees, contribution timing or compounding frequency. Providers often project net of their own charges and may compound annually. Neither convention is wrong, but they are not comparable without checking.
Compare the cost of investing
The investment fee calculator separates direct charges from the growth difference and compares two fee levels on the same monthly saving plan.
Deposit schedule
The monthly budget is grouped into equal deposits per selected compounding period. Choose monthly compounding for a monthly deposit schedule. A final partial period earns growth but receives no deposit. See the exact model and verification method.