Guide
Retirement planning basics
Last updated: May 2026
This guide explains how to use the calculator inputs as a planning system. The goal is not to deliver personalized advice or fixed predictions. It is to build a repeatable process where your numbers are transparent, adjustable, and easy to stress test.
Practical retirement planning workflow
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01. Define a practical spending target in today-dollar terms.
Start with a realistic after-tax spending target for your intended lifestyle. Split it into fixed needs versus flexible wants. The calculator assumes one number for annual spending, so the closer this number is to reality, the more useful every downstream estimate will be.
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02. Estimate your savings base and path.
Enter current savings, monthly contributions, expected return, and volatility assumptions. These values shape the FIRE target and the projected portfolio path in the core simulator.
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03. Set the retirement age and bridge timeline.
Long retirement windows are usually where small mistakes get expensive. Confirm whether Social Security, Medicare, or other income starts before, at, or after your target age.
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04. Choose an initial withdrawal rate and test alternatives.
Use several safe withdrawal rates rather than one favorite number. A lower rate usually requires a larger portfolio but improves flexibility under weak market years.
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05. Run Monte Carlo and read the success rate as a stress test.
Success percentage is a distribution signal, not an outcome promise. Treat it like an estimate of how often a scenario survives over time.
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06. Update assumptions each year.
Use the annual review flow to revisit inflation, contribution, and spending inputs. Static numbers create static comfort, not accurate planning.
Worked example: 45-year-old aiming for 60
A person is 45, has $310,000 saved, contributes $2,300 monthly, assumes 7.0% return, 3.0% inflation, spends $64,000 a year, and targets 3.5% withdrawal. They test retirement at age 60 and then compare age 59 and 61 for sensitivity.
The workflow outcome usually shows whether the FIRE number is likely a cushion or a target date pressure point. If success rate is low at age 60, compare: lower spending by 10%, delay one year, or move from a 4.0% to 3.5% target. These changes often matter more than small return tweaks.
The calculator can show a higher projected portfolio at 60 with stronger contributions, but if sequence risk is rough right after retirement, a long timeline can still require contingency cash or flexible spending actions. This is why sensitivity tests and bridge planning remain part of the process.
Checklist
| Planning area | What to set in the calculator | Review cadence |
|---|---|---|
| Spending target | Current annual after-tax spending estimate | Quarterly check if income changes |
| Contribution schedule | Monthly savings amount and expected step-ups | Update with each raise |
| Retirement age | Target age and reason for stop | Review every year |
| Withdrawal rate | 3.0% to 4.0% stress test | After major market moves |
| Monte Carlo tolerance | Run with current assumptions | Every six months to yearly |
Common mistakes
- Using gross spending instead of estimated after-tax spending.
- Assuming inflation is always close to 2% when medical or housing inflation can drift higher.
- Testing only one withdrawal rate and treating one successful run as proof of certainty.
- Skipping bridge years between retirement and Social Security or Medicare starts.
- Ignoring tax position changes when incomes switch from wages to withdrawals.
Monte Carlo interpretation
A higher success rate does not guarantee an outcome; it means a larger share of simulated return paths stayed sustainable under your assumptions. If the rate is volatile across nearby assumptions, that uncertainty is a valid planning signal to build flexibility into spending or buffers.
FAQ
Is one calculator run enough to make a retirement decision?
No. Use it as one checkpoint, then re-run with changed assumptions, contribution timing, and spending flexibility.
Should I keep spending constant in current dollars?
It is a practical baseline. It keeps the model simple and makes assumption testing more transparent. Add inflation growth separately in the next pass.
Can the FIRE number be treated as a target budget limit?
Think of it as an estimate of required capital under a chosen withdrawal rate and assumptions. It is not a guaranteed minimum or guarantee of success.
Related planning links
Next planning steps
Use these pages to test one major planning lever at a time.