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Advanced Investment Growth Calculator
Project long-term portfolio growth with recurring contributions, fees, inflation, taxes, and side-by-side scenarios.
CompoundLab
Financial calculators that show the assumptions behind the number
CompoundLab helps you test long-term money decisions with clearer context. Compare investment growth, FIRE targets, retirement withdrawals, rent vs. buy choices, and mortgage payoff scenarios — without hiding the assumptions that drive the result.
Calculator library
Start with the decision you are trying to understand
Each calculator focuses on a specific planning question. Some are about growing a portfolio. Others are about retirement, housing, or whether extra cash should go toward a mortgage or into the market. The goal is not to predict the future perfectly. It is to make the tradeoffs easier to see.
Why assumptions matter
The final number is only useful if you understand what moved it
A calculator can make a result look precise even when the future is uncertain. CompoundLab is built to show the inputs behind the output, so you can test how sensitive a result is to time, returns, fees, inflation, contributions, and withdrawal choices.
Time can matter more than a higher return
A long investment horizon gives compounding more room to work. That is why a lower-return scenario over many years can still beat a higher-return scenario over a short period.
Small assumptions can create large gaps
Changing an expected return from 6% to 7%, adding a 1% fee, or switching from nominal to inflation-adjusted results can materially change the outcome. The point is not to find the perfect input. The point is to understand the range.
Some decisions are not just mathematical
Paying off a mortgage, buying a home, or retiring early also depends on risk tolerance, flexibility, liquidity, and personal comfort. The calculators show the financial tradeoff, but they do not replace judgment.
Examples
A few simple ways assumptions change the result
These examples are not recommendations. They show why it is worth testing more than one scenario before relying on a single output.
Example
Monthly investing over time
Inputs
$500 invested monthly
7% annual return
30-year horizon
Output
Final valueabout $567,000
Total contributions$180,000
Estimated growthabout $387,000
Note
The result is driven less by one perfect investment choice and more by repeated contributions over a long period.
Example
One percentage point can matter
Inputs
$10,000 starting balance
$500 monthly contribution
30-year horizon
Output
6% returnabout $537,000
7% returnabout $609,000
8% returnabout $694,000
Note
The exact future return is unknowable, which is why scenario comparison is more useful than relying on one assumption.
Example
Fees quietly compound too
Inputs
$10,000 invested once
30-year horizon
7% annual market return
Output
No annual feeabout $76,000
1% annual feeabout $57,000
Note
A fee does not only reduce this year’s return. It also reduces the money that remains invested for future growth.
Insights
Read before you choose your assumptions
The calculators are more useful when the assumptions are realistic. These guides explain common planning inputs such as real returns, fees, withdrawal rates, mortgage tradeoffs, and inflation.
Mortgage Payoff vs. Investing: When the Math Changes
Compare paying extra toward a mortgage versus investing the same cash flow, and learn how interest rates, taxes, liquidity, risk, and time horizon change the result.
FIRE Number Explained: Why 25x Expenses Is Only a Starting Point
Understand how the FIRE number is calculated, why the 25x rule comes from a 4% withdrawal assumption, and why inflation, taxes, and flexibility matter.
What Return Assumption Should You Use in a Compound Interest Calculator?
Learn how to choose realistic investment return assumptions, compare conservative and optimistic scenarios, and avoid overconfidence in long-term projections.
Clear methodology, visible limitations
CompoundLab calculators are educational planning tools. Each major calculator has a methodology page explaining the inputs, formulas, assumptions, limitations, and example calculations behind the result.