Guardrail is one of the four rules in Expenses → Spending strategy. Real retirees don't spend a fixed amount no matter what markets do. They ease off in bad stretches and loosen up in good ones. The guardrail models that flexing instead of pretending spending is rigid.
It sits second on a ladder of four: Fixed plan never reacts, the guardrail nudges your flexible spending when your withdrawal rate strays, and VPW / % of balance recompute your spending from the balance outright. It's the option for someone who wants to keep a plan and still answer to the market.
How it decides
Each simulated year compares your current draw rate against two bands:
- Above the upper guardrail (spending is stretching the portfolio) → trim the flexible slice of spending by the cut step (e.g. 10%).
- Below the lower guardrail (you clearly have room) → raise it by the raise step.
- A floor and ceiling bound how far cumulative cuts or raises can drift from your original plan, and cuts can heal (reversible) when markets recover.
What it may touch
Only the flexible share of Recurring spending that you declare: dining out, travel, hobbies. The rest of Recurring, plus Housing and Medical, is treated as essential and is never trimmed. At 100% the whole Recurring budget flexes; lower it if part of your budget is untouchable.
That field sits above the rule's own knobs because it isn't only the guardrail's. The same split is the essential floor VPW and % of balance can never spend below. It is one budget fact, read two ways.
The presets (Conservative / Moderate / Aggressive) are one axis: how hard the guardrail protects the plan versus your lifestyle. Conservative reacts sooner and cuts deeper; Aggressive reacts late and holds a high floor.
A higher success rate bought by spending cuts is only a good deal if you can see the cost. The Spending strategy panel reports both halves, including what a "trip" of the guardrail means in dollars per month.
Why you can't add it to VPW
You pick one rule, not a rule plus a modifier. VPW and % of balance already recalculate your spending from your balance every year, so layering the guardrail on top would react twice to the same signal. You could no longer tell which one moved your spending. Choosing one of them is choosing not to use the guardrail.
To see what you gave up, run Explore → Compare spending strategies: the Guardrail row is scored with the knobs you set here, whichever rule you currently have picked.