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MoneyBasis

Formulas and assumptions

How MoneyBasis calculates results

Explore the formulas, assumptions and sources behind each estimate. Your inputs provide the starting point; the calculation runs in your browser.

A magnifying glass examining a calculation

Retirement Calculator

What it estimates

This calculator estimates retirement savings using your age, current balance, contributions, retirement age and expected-return assumptions. Projected values are estimates, not guaranteed outcomes.

How it calculates

Estimated withdrawal ≈ nest egg × selected withdrawal rate / 12

Accumulation uses nominal annual returns compounded monthly. Withdrawal rate is an adjustable planning assumption, not guaranteed income. Monthly spending is entered in today’s dollars and inflated to retirement, then raised annually.

Inputs

Current age · Retirement age · Current savings · Monthly contribution · Expected return

Included / not modeled

Included

  • Contributions until retirement
  • Assumed investment return
  • Inflation-adjusted spending target
  • Illustrative withdrawals and drawdown

Not modeled

  • Social Security and pensions
  • Taxes
  • Market volatility
Assumptions & limitations
  • Contributions continue until retirement age.
  • The expected return is a user-adjustable assumption, not a predicted market result.
  • The drawdown illustration uses a nominal annual return capped at 5% as a planning assumption. It is not a forecast.
  • Social Security, pensions and taxes are excluded. Inflation adjusts the spending target; portfolio charts show future nominal dollars.

Sources

Open Retirement calculator →