The main assumptions
- Current savings: the starting balance that compounds from today.
- Future contributions: recurring additions before retirement.
- Expected return: the assumed annual growth rate before or after inflation, depending on the calculator setting.
- Inflation: the rate used to estimate future purchasing power.
- Withdrawal rate: how much is taken from savings during retirement.
- Retirement length: the number of years the savings may need to support spending.
Nominal vs real projections
A nominal projection shows future currency amounts. A real projection adjusts for inflation and is usually easier to compare with today's spending power. Mixing nominal returns with real spending targets is one of the most common retirement-planning errors.
What the calculator cannot know
Retirement calculators cannot predict market returns, tax law, pension changes, health costs, inflation shocks, housing costs or lifespan. A useful calculator shows assumptions clearly and make it easy to test alternative scenarios.
Better scenario testing
- Run a conservative return scenario and a higher-return scenario.
- Test retirement ages that are earlier and later than your preferred date.
- Compare fixed contributions with contributions that increase over time.
- Look at inflation-adjusted spending, not just the final account balance.
Assumptions that dominate retirement estimates
Three assumptions usually dominate retirement projections: return, inflation and withdrawal rate. A portfolio expected to earn 6% nominal with 2.5% inflation has an estimated real return of about 3.41%. Using 5% nominal instead of 6% over several decades can reduce the projected balance substantially.
A 4% withdrawal example means withdrawing 40,000 from a 1,000,000 portfolio in the first year, then adjusting later withdrawals under the chosen assumption. It is a planning convention, not a guarantee. Taxes, fees, sequence of returns and country-specific pension rules can all change the outcome.
Useful calculators
FAQ
What return should I use?
Use a scenario assumption, not a guarantee. Many users test several return assumptions to see how sensitive the result is.
Should I include inflation?
Yes if you care about purchasing power. A high future balance can still buy less if prices rise substantially.
Is a withdrawal rate safe?
No withdrawal rate is universally safe. It depends on market returns, fees, taxes, spending flexibility and retirement length.
References
- Investor.gov: financial tools and calculators, accessed 2026-05-16.
Last reviewed: 2026-05-16.