What-if scenarios: ask a question about your plan without changing it

Most planning tools make you edit the plan to ask a question, then remember to change it back. What-ifs are a separate layer: they store only the difference, so your real plan stays intact and the what-if never goes stale.

Killion virtual scenarios screen running a Monte Carlo projection, showing the outcome range across simulated paths.

A what-if is a diff, not a copy

Copying a plan to test an idea creates a second thing to maintain. A month later your income has changed, your balances have moved, and the copy is quietly wrong, usually in the direction that makes the idea look better than it is.

Killion stores a what-if as the set of changes you made. Everything else is read live from your real plan, so when a new month of budget data lands, every what-if moves with it.

The switches you can combine

Each switch is independent and they stack, which is what makes the feature useful for the questions people actually have, which are rarely about one variable.

  • Retirement age. Move the date earlier or later and see the whole trajectory shift.
  • Withdrawal rule. Swap a rigid rule for guardrails without touching the base plan.
  • Lifestyle creep. Let spending grow faster than inflation and watch the effect compound.
  • Horizon. Plan to 95 instead of 90 and see what longevity risk costs.
  • Market shock. Schedule a crash in a specific year to isolate sequence-of-returns risk.

Paired comparison is the part that matters

Comparing two plans by their median outcomes hides the thing you want to know. A change that raises the median but helps in only 55% of worlds is a very different proposition from one that helps in 95% of them.

When two runs share the same market draws, Killion compares them world by world and reports how often the change actually helped. That converts "the median went up" into "this was better in 87% of the futures we simulated", which is a claim you can act on.

The research behind it

  • Withdrawal strategies: Pick a spending rule (the 4% rule, guardrails, a fixed percentage) and watch the projection follow it.
  • Backtesting: Run your portfolio and withdrawal rule through every real market start year since 1928 and get a survival rate for each.

Frequently asked questions

Does a what-if change my real plan?
No. A what-if stores only the switches you flipped and reads everything else from your plan, so your plan is never modified.
How many plans can I compare at once?
Up to four pinned plans, shown together on every chart.
What is a paired comparison?
Running two plans against the same simulated markets and comparing them world by world, so you learn how often a change helps rather than only whether the average improved.
Try it in the live demoSee pricing