Retirement Monte Carlo Simulator

One average return tells you almost nothing. A Monte Carlo simulation tests your plan against a thousand different market lifetimes and answers the only question that matters: how often does your money last?

Most retirement math quietly assumes your investments earn the same tidy percentage every single year. Real markets never do that. They crash the year you retire, boom a decade later, and deliver inflation in uneven bursts. A Monte Carlo simulation drops that fantasy: it runs your exact plan — your spending, your accounts, your Social Security and taxes — through hundreds of different sequences of real market history, then counts how many of those lifetimes you finish with money still in the bank. That count, expressed as a percentage, is your probability of success.

What a success rate really means

An 85% success rate does not mean you'll end up with 85% of your money. It means that in 85 of every 100 simulated market lifetimes, your plan funded your spending all the way through — and in the other 15 it ran short before the end. It's a batting average against history, not a guarantee. That framing matters, because it reframes retirement from a single yes/no answer into a margin of safety you can widen or narrow on purpose: spend a little less, work one more year, or claim Social Security later, and watch the odds move.

Why the average is the dangerous number

The reason averages mislead is sequence-of-returns risk. Two retirees can earn the identical average return over 30 years and end up in completely different places — if one of them hit a savage bear market in the first few years, while they were selling shares to cover living expenses, they may never recover, because there were fewer shares left to ride the rebound. The order of the returns, not just their average, decides who runs out. Monte Carlo is the only common tool that actually surfaces this risk, because it looks at the whole path, year by year, instead of collapsing it into one number.

What a good number looks like

Most planners aim for a success rate somewhere around 85% to 95%. Chasing a perfect 100% is usually a sign you're being too cautious — leaving real money and years of freedom on the table to insure against market lifetimes that have never happened. The sample below is deliberately a tight plan: it lands near a coin flip, exactly the situation where the simulator earns its keep, showing you which small changes push the odds back into safe territory. retireclarity runs 1,000+ trials over about a century of market history, so your plan is tested against real booms, busts, and inflation rather than a single guess.

Want the deeper background first? Read how Monte Carlo retirement simulation works. Or jump straight to the full Monte Carlo simulator.