Investment Calculator

Estimate compound growth, separate contributions from growth, model simple fee drag and inflation-adjusted “today’s dollars,” and compare a few scenarios side-by-side. Quick inputs first, deeper detail only if you want it.

For educational purposes only. This calculator provides general estimates and does not provide financial, trading, tax, or legal advice.

Runs locally in your browser. No account. No signups.

Quick Projection

Enter a simple set of assumptions to estimate a future value and see how much comes from contributions vs growth. This is a simplified model designed for comparison, not prediction.

Starting balance for the projection.
Modeled at the end of each month in Quick mode.
Constant return assumption used for the math (illustrative).
Converted to months (years × 12) for monthly compounding.
Educational estimates only. This investment calculator performs mathematical projections based on user-entered values and simplified assumptions (such as contribution amounts, rate of return, time horizon, and compounding frequency). It does not provide personalized investment, financial, tax, legal, or trading advice, and it does not account for market volatility, risk tolerance, inflation, fees, taxes, behavioral factors, drawdowns, sequence-of-returns risk, or individual circumstances. Projected outcomes are hypothetical illustrations — not predictions, guarantees, or recommendations. Calculations run locally in your browser. See Disclaimer, Privacy Policy, and Terms of Use.

Methodology & Limits (Quick)

  • Compounding: monthly compounding with a constant annual return assumption.
  • Contributions: modeled at end of month in Quick mode.
  • What’s excluded: taxes, account rules, volatility/sequence risk, and changes in contribution behavior.

How This Investment Calculator Works

This tool is designed for clear scenario math, not predictions. It uses a simplified model: monthly compounding with a constant assumed annual return and repeating monthly contributions. The main value is consistency — when you change one input, you can see how the output changes under the same rules.

What it shows: a projected ending value, how much you invested (initial + contributions), and the remaining difference labeled as estimated growth within this model.
What it does not do: it does not forecast markets, model taxes, or reflect account-specific rules. Results are arithmetic outputs from your assumptions.

The Core Inputs (And Why They Matter)

Investment projections are sensitive to a few variables. This calculator centers those inputs so you can test them directly:

  • Initial investment: the starting balance. Earlier dollars generally have more time to compound in the model.
  • Monthly contribution: the repeating deposit amount. Over long horizons, this often drives outcomes more than small return tweaks.
  • Return rate: a constant annual percentage used for the math. Real returns vary year to year, but a constant rate is useful for comparisons.
  • Time horizon (years): compounding is time-dependent. Longer timelines can change outcomes dramatically in simplified models.

Quick Example (Illustrative Only)

Suppose you start with $5,000, contribute $200/month, assume a constant 7% annual return, and run the model for 20 years. You’ll contribute $48,000 over time (200 × 12 × 20), plus the initial $5,000 — and the model attributes the remainder of the projected ending value to growth from compounding.

  • Total contributed = 200 × 12 × 20 = $48,000
  • Total invested = initial + contributions
  • Estimated growth = projected value − total invested

Note: this is model math. Real portfolios experience uneven returns, different contribution timing, and taxes/fees that vary by product and account type.

Contribution Timing

In the real world, contributions can land at different times (start of month, end of month, or irregularly). This calculator uses end-of-month deposits by default in Quick mode for consistency. In Adjust mode, you can switch timing to see how earlier deposits slightly increase compounding time in the model.

Fees (Simplified “Fee Drag”)

Fees matter because they reduce what effectively compounds. To keep the model understandable, this calculator uses a simplified approach: if you enter an annual fee (such as an expense ratio), it computes an illustrative net rate as (return − fee). That’s not how every fee works in every product, but it’s a useful comparison tool.

Why small fees can add up (Conceptual)

A difference that looks small (for example, a fraction of a percent) is applied year after year in long-horizon compounding. This tool helps you test that sensitivity using the same baseline assumptions.

  • Compare the same return with fees set to 0% vs a small fee.
  • Hold everything else constant so you isolate the impact.
  • Use the Compare tab to view scenarios side-by-side.

Inflation-Adjusted “Today’s Dollars”

A future dollar is not always equal to a current dollar in purchasing power. If you enter an inflation rate, the calculator also computes an inflation-adjusted estimate by discounting the nominal ending value into “today’s dollars.” This helps with comparisons across timelines — it is a general illustration, not a forecast.

Contribution Growth (Optional)

Many people increase contributions over time (for example, after raises). The contribution growth option illustrates that idea by increasing the monthly contribution once per year by the percentage you enter. This is a simplified step-up model intended for scenario testing.

Best way to use this calculator: change one input at a time (years, rate, fees, contribution) and compare results. That reveals what the model is most sensitive to.
Reality check: real investing involves variability (good years/bad years), taxes, and account/product rules. This tool intentionally simplifies those so the math is readable.

What This Model Excludes (On Purpose)

Exclusions are not “missing features” — they’re a tradeoff for clarity. This calculator does not model:

  • Taxes: different accounts and jurisdictions can change outcomes materially.
  • Sequence risk / volatility: returns are not constant in real markets.
  • Product/account rules: contribution limits, withdrawal rules, penalties, and restrictions.
  • Irregular behavior: pauses, changing deposit schedules, or large one-time contributions beyond the modeled pattern.

For related tools, explore the Retirement Calculator, Savings Goal Calculator, and Net Worth Calculator.

Investment Calculator FAQ

Does this investment calculator store my data?

No. The calculator runs locally in your browser. Calculator inputs are not collected for signups and are not stored by FinFormulas. Cookies/identifiers may be used for analytics and advertising as described in our Privacy Policy.

Is the result exact?

No. Results are estimates based on the numbers you enter and simplified assumptions. Real-world returns, fees, taxes, timing, and account rules can differ.

Why does the calculator assume constant returns?

A constant return assumption keeps the math consistent so you can compare scenarios cleanly. It’s best used for sensitivity testing, not forecasting.

How do fees affect results?

If you enter an annual fee (such as an expense ratio), the calculator reduces the assumed return rate by that fee for an illustrative fee-adjusted estimate. Real fee structures can be more complex.

What does inflation-adjusted mean?

Inflation-adjusted values are expressed in “today’s dollars” by discounting future values using the inflation rate you enter. This is a general illustration to support comparisons — not a prediction.

Will this tell me what I should do with my money?

No. This tool provides arithmetic outputs from your inputs so you can compare scenarios. It does not provide individualized guidance or recommendations.

Reviewed & Updated

Calculator logic and on-page content reviewed for clarity and educational accuracy. Last review: December 2025.