The retirement calculator separates accumulation from drawdown because the same return assumption does not play the same role in both phases. Before retirement, users are adding money. After retirement, they are withdrawing it.
Before retirement
Current savings grow at the selected pre-retirement return while monthly contributions are added over time. This creates the estimated portfolio available at the chosen retirement age.
At retirement
The desired retirement income is compared with any other expected income. The gap is the amount the portfolio needs to support. Inflation raises that spending need over time.
After retirement
The model simulates withdrawals against the remaining portfolio while applying a retirement return assumption. This helps estimate whether the money lasts through the selected life expectancy.
A worked example
A person who retires later may benefit three times: more contributions, more years of growth, and fewer years of withdrawals. That is why changing retirement age can move the result much more than people expect.
What we intentionally simplify
The calculator does not model tax brackets, account withdrawal order, healthcare shocks, government-benefit rules, or sequence-of-returns risk in full detail. It is a planning model, not a complete retirement plan.
Why inflation appears twice in the conversation
Inflation affects the spending target before retirement and the withdrawals after retirement. A plan can look comfortable in today's dollars while becoming thin once future spending is properly adjusted upward.
Where users can misread the model
A portfolio that lasts in a smooth-return simulation may still struggle if losses arrive early in retirement. That is why the tool should lead to stress testing, not to overconfidence.
Why retirement age is such a powerful input
Changing retirement age can improve the plan from three directions at once: more years to save, more years to compound, and fewer years to withdraw. That is why a modest delay can sometimes matter more than a small return increase.
What readers should compare
Do not look only at the portfolio size on retirement day. Compare the income gap, supported monthly income, years funded, and the effect of less friendly assumptions. A strong plan is not merely large. It is resilient.
Why “money lasts until” is only one answer
A portfolio that technically lasts can still leave little flexibility. The model is more useful when users also ask how much spending it supports, how sensitive the result is to inflation, and which lever creates the widest margin.
How to use the result well
Focus on the gap, then test several levers: monthly contribution, retirement age, retirement spending, expected return, and other income. A robust plan should still make sense when the assumptions become a little less friendly.
Related tools
See the Retirement Calculator, SWP Calculator, and Retirement Planning Guide.