The Sketch uses geometric compounding. Your savings grow along three steady paths — conservative, baseline, and upside — at 1.5%, 3.5%, and 5.5% a year above inflation, anchored to long-run averages. They form your Estimated Floor, middle projection, and Estimated Ceiling. Every figure is in today's dollars, and each boundary sets aside a flat 8% for taxes. Market outlook, inflation, and your actual tax rules are modeled in the Studio by the full engine.

Plan-Through Age sets how long the money has to last. It's the one input that isn't about how hard your plan works, but how long — and it reshapes everything downstream. A shorter retirement means each dollar covers fewer years, so the same capital safely supports more spending: your Estimated Floor, Estimated Ceiling, and target all rise. A longer retirement spreads the same capital thinner, and all three settle lower. Set it to the age you genuinely want to be covered through — it's an honest assumption, not a dial to make the numbers look better.

Before a Reveal, your Floor and Ceiling are quick estimates. Your Estimated Floor assumes cautious growth and a lower withdrawal rate. Your Estimated Ceiling assumes strong growth and a higher one. Your Spending line is different: it shows the savings your spending would need, using the 4% rule as a simple yardstick, and it moves with your plan-through age like the other two. So the three lines answer three plain questions: how low it could go (Floor), how high it could reach (Ceiling), and what your spending costs in savings (Spending). Reveal your Range to test them. Your tested Floor is the most you can spend and still get through the stress histories your Load Test asks for. Your tested Ceiling is the most you can spend while, on average, 90 of every 100 planned dollars still arrive.