How to Compare Investment Growth Without Hiding the Assumptions
By MoneyCalc · Educational scenarios
Two investment projections are only comparable when they use the same end date, deposit schedule and definition of return. A larger final number may come from putting in more money rather than earning a better return.
1. Keep the same end date
To compare starting today with waiting five years, use a common finish date. A 20-year plan today gives a delayed start only 15 years of investing. Giving both scenarios 20 invested years answers a different question because they finish at different dates.
State what happens to money during the delay. Our cost-of-waiting model keeps the starting lump sum in zero-interest cash and assumes missed monthly deposits are not saved. If you would save those deposits elsewhere, include that other balance before comparing total wealth.
2. Separate deposits from growth
Waiting five years to make $300 monthly contributions means 60 fewer deposits, or $18,000 less contributed. The difference between final balances therefore is not all lost interest. Subtract the missed contributions to isolate the remaining growth difference.
At a zero return, the gap in this scenario is exactly the missing deposits. At a positive constant return, earlier deposits have more time to grow. At a negative return, the growth difference can favor waiting. These are mathematical scenarios, not claims about the best time to enter a market.
3. Use the same rate convention
A nominal annual rate compounded monthly is not the same as an effective annual return. The new planning tools convert an effective annual return to a monthly rate using (1 + annual return)^(1/12) − 1. A 5% effective annual return therefore compounds to 5% over twelve months.
Check whether deposits occur at the beginning or the end of each month. Our timing comparison uses month-end deposits. Also distinguish a constant modeled rate from actual returns, which vary. A projection cannot remove volatility or tell you which future return will occur.
4. Compare purchasing power, not just future dollars
Future money and today's money are different units. With a 5% nominal return and 3% inflation, the exact real return is 1.05 ÷ 1.03 − 1, or about 1.94%. Simply subtracting the two rates gives a useful approximation, but not the exact result.
The table isolates one lump sum so contributions do not obscure the comparison. Inflation is a user-selected assumption. A broad consumer price index may not match your own mix of expenses. Fees and taxes also affect results, so label a gross projection clearly or use a consistent net-return assumption.
| Annual inflation | Future nominal balance | Purchasing power today |
|---|---|---|
| 0% | $16,288.95 | $16,288.95 |
| 3% | $16,288.95 | $12,120.51 |
| 5% | $16,288.95 | $10,000.00 |
Try it with your numbers
- Cost of Waiting to Invest
At 0% return, a five-year delay in $300 monthly deposits creates a $18,000.00 gap. Change the assumptions yourself.
- Real Return After Inflation
Translate future nominal dollars into purchasing power.
- Compound Interest Calculator
Explore a deposit-and-growth scenario.
- ROI Calculator
Compare an initial and final value, including annualized return.
Sources and scope
Examples are illustrative calculations, not market forecasts or individualized advice. Background sources do not endorse MoneyCalc. See our methodology and limitations.