Compound interest means returns can earn additional returns. Time and consistent contributions often matter as much as the initial balance, while the assumed rate remains uncertain.
The growth formula
A basic compound-growth model applies the rate at regular intervals. Contributions can be added monthly or annually, depending on the account and the calculator inputs.
What changes the result
A higher rate increases projected growth, but it also increases uncertainty. More frequent compounding can slightly change the result. Starting earlier gives the balance more time to grow.
Use projections carefully
A calculator is useful for comparing scenarios, not promising a return. Compare conservative, expected and lower-return assumptions, and account for taxes, fees and inflation when planning.
- Use a rate that matches the period unit.
- Separate contributions from investment returns.
- Review the plan when your contribution or time horizon changes.
Frequently asked questions
Are compound-interest results guaranteed?
No. The output depends on the rate assumption. Savings products, investments and fees can change the actual result.
Should I include monthly contributions?
Include them when you regularly add money. The contribution schedule can materially change the projected balance.