Separate growth from contributions
A future-value estimate can grow because the investment earns returns, because new money is added, or both. Showing these pieces separately makes the result easier to understand.
If regular contributions are included, note whether they are added at the beginning or end of each period. The timing changes the final balance.
Treat rates as scenarios
A fixed annual percentage in a calculator is a simplifying assumption. Real investment returns change over time and can include losing periods.
Run conservative, middle, and optimistic rates. A plan that needs the optimistic rate to work may need more savings, more time, or lower future spending.
Account for real-world friction
Taxes, fees, inflation, withdrawal timing, and account rules can all reduce the useful value of a projected balance.
Use compound interest calculators for education and planning conversations. Confirm investment, tax, and retirement choices with qualified professionals.