Practical guide
Understanding compound savings growth — two-scenario comparison
Everyday editorial team · GEOINNOVATION CO., LTD · Published · Updated
What this calculation is for
Compound growth shows how a starting balance and recurring deposits may develop over time. Comparing a deposit increase with a rate increase can reveal which assumption has more influence. Keep savings-account assumptions separate from risky investment-return assumptions.
How the method works
The starting balance grows at a monthly-equivalent rate and deposits are added at month-end. Where compounding frequency is editable, it converts a nominal annual rate using that frequency. Detailed tools also show proportional annual fee effects and purchasing power after the entered inflation rate.
A worked example
A $1,000 opening balance plus $100 each month contains $2,200 of contributions after one year. An ending balance above $2,200 represents modeled growth; it should not be confused with the full account balance.
Assumptions and real-world differences
Rates, contributions and fees are held constant. Taxes, changing bank terms, investment losses and irregular deposit timing are not automatically included. A CD penalty is a separate alternative rather than a deduction from its normal maturity amount.
Building two independent scenarios
Scenario A and Scenario B each have a complete set of inputs for this compound savings growth calculation. Change several inputs in B when comparing genuinely different plans, then inspect the B-minus-A headline difference and the detailed rows. When multiple inputs change, the total difference cannot be attributed to just one of them.
Reproduce this tool’s example
These fixed example inputs are independent of edits you make above. Enter them in this tool to reproduce the result, then replace them with your own assumptions.
- Scenario A — Starting balance
- 10,000 $
- Scenario A — Monthly deposit
- 500 $
- Scenario A — Annual nominal return or APY
- 5 %
- Scenario A — Years invested
- 15 years
- Scenario A — Compounding periods per year
- 12 periods
- Scenario A — Annual inflation assumption
- 2.5 %
- Scenario A — Annual fee rate
- 0.25 %
- Scenario B — Starting balance
- 12,500 $
- Scenario B — Monthly deposit
- 500 $
- Scenario B — Annual nominal return or APY
- 5 %
- Scenario B — Years invested
- 15 years
- Scenario B — Compounding periods per year
- 12 periods
- Scenario B — Annual inflation assumption
- 2.5 %
- Scenario B — Annual fee rate
- 0.25 %
Scenario B result: $156,323.73
Scenario A: $151,234.2. Projected ending balance.
- Scenario A main result: $151,234.2
- Scenario B main result: $156,323.73
- Numeric difference (B − A), in result units: 5,089.53
Frequently asked questions
- Is an advertised APY the same as a nominal rate?
- No. APY already reflects compounding; check the field description before entering a quoted rate.
- Are deposits made at the beginning of the month?
- These projections use month-end deposits unless the specific tool states otherwise.
- Why is this different from the one-factor comparison?
- The one-factor tool changes only starting balance. This version lets all model inputs differ, so it is more flexible but does not isolate the effect of any single change.