A steady SWR assumes you spend the same real amount every year no matter what markets do. A flexible SWR assumes you'll respond: ease back a little when your portfolio falls a long way, and spend a bit more when it does well. Because you're not locked into overspending through a downturn, you can safely *start* from a higher rate — typically 1.5–2 percentage points higher.
| Fixed (steady) spending | Flexible (guardrails) spending | |
|---|---|---|
| Starting withdrawal rate | Lower — must survive the worst market | 1.5–2pp higher |
| In a downturn | Hold spending (higher risk of running out) | Trim ~10% at the rail (never below your essentials floor) |
| In a boom | Hold spending | Raise spending ~10% |
| Trade-off | Predictable income, but you leave money unspent to be safe | More income on average, but you must accept real cuts in bad years |
How the guardrails work
The planner uses the well-known Guyton-Klinger rules. Your withdrawal (net of the Age Pension) is checked against upper and lower rails:
- If it drifts about 20% above your target rate (portfolio fell), you cut spending ~10%.
- If it drifts about 20% below (portfolio grew), you raise spending ~10%.
- An essentials floor stops cuts from ever taking you below your basic needs.
The honest trade-off: a flexible plan 'lasts' partly *because* you cut. In a rough market the flexible spend can dip below the steady level for years — that's the cost of the higher starting rate.