Why are the rungs cumulative?

Because the ladder measures one quantity — everything you could draw on — against three thresholds, rather than dividing your money into four pots. Money first fills Survival, then carries on into Sustenance, then into Sufficiency. Whatever you hold counts toward the level it reaches and toward every rung above it, and the end of the ladder is your FI number, the same figure the rest of your plan uses.

How the three thresholds are set

1. Survival ends at your essential monthly spending times the months you choose.
2. Sustenance ends at that, plus your full monthly spending times twelve times the years of runway you choose.
3. Sufficiency ends at your FI number. In the rare case where a very long runway would reach past it, the top is held at Sustenance’s level instead, so no rung ever has a negative target.

Each rung is then judged on its own slice: how far your total has climbed through the gap between the threshold below it and its own. That is the percentage you see beside each rung.

Why it matters when you move a slider

The top of the ladder is fixed at your FI number, so the three targets always add up to it. Raising Survival or Sustenance therefore takes the same amount out of Sufficiency’s slice. The Sufficiency card says so in its own words: raising Survival or Sustenance raises what they need, and because the rungs are cumulative, it takes the difference out of this one. After a change, the readout under the bar marks each rung whose target moved with an arrow and target up or target down.

Reading the bar

Segment widths are eased so the small early rungs stay readable; the fill inside each one, and every figure in the readout, is exact. Each readout row gives the amount held “of” its target (a full rung shows one figure), a word with a percentage and, while a rung is short, the amount still to go. Surplus has no target, so its row reads No target — this is what is left over.