Diane has $300,000 sitting in a brokerage account and one question she can't stop asking: if she pulls $2,500 a month, when does it run out? Most people guess. They take the balance, divide by the withdrawal, and call it a day. That math says $300,000 divided by $30,000 a year equals 10 years. Clean. Simple. And wrong.
Here's what that shortcut ignores: the money she hasn't withdrawn yet is still earning a return. At a 5% annual return, the same $300,000 balance with the same $2,500 monthly withdrawal doesn't last 10 years. It stretches closer to 14 years. That's roughly four extra years of income she'd never have planned for if she trusted the divide-and-done estimate. Four years is the difference between a plan that holds and a plan that leaves her short.
The reason is a quiet tug-of-war happening every month. Your return is pulling the balance up. Your withdrawal is pulling it down. Early on, when the balance is large, the return is winning more battles than you'd expect. A 5% return on $300,000 is $15,000 a year in growth, against $30,000 a year going out the door. The account still shrinks, but at half the speed the naive math predicts, because growth is quietly refilling half of what she takes out.
Then the curve turns. As the balance drops, the return earns less in raw dollars, while the withdrawal stays flat at $2,500. When the balance falls to $150,000, that same 5% return throws off only $7,500 a year against the unchanged $30,000 going out. The two forces cross. Once the withdrawal permanently outpaces the growth, the balance falls faster and faster, and the last few years drain quicker than the first few. This is why drawdown timelines look like a ski slope, not a straight line: gentle at the top, steep near the bottom. It's also why a one-line division can be off by years in either direction, and why the same balance can feel either comfortable or fragile depending on a single return assumption.
Change one input and the whole picture shifts. Raise the return to 7% and the same balance and withdrawal can last well beyond 20 years. Drop it to 3% and you're back near that 10-year cliff. Bump the withdrawal to $3,000 a month at 5% and you lop about three years off the timeline. The point isn't any single number. The point is that withdrawal amount, return, and time are locked together, and you can't move one without moving the others. Pull harder now and you finish sooner; accept a leaner monthly check and the money rides longer. This calculator lets you watch that trade-off in real time instead of guessing and hoping the balance holds.