Decision path
Retire on Your Terms: A Savings-to-Simulation Path
“Can I retire?” is really two questions: how much do I need to save each month, and how likely is that plan to survive real markets? This path answers them in order. Step 1 works backwards from your target to a required monthly rate; step 2 feeds that rate into a full Monte Carlo retirement simulation. Your inputs carry forward automatically and stay editable at every step.
Step 1
Find your required monthly savings
Set the nest egg you want, what you already have, and your time horizon — all in today's dollars, using real (inflation-adjusted) returns. You get a deterministic monthly rate under three return scenarios plus a Monte Carlo rate calibrated to your chosen success probability.
Check your inputs.
Step 2
Stress-test the full retirement plan
Your savings, return, and volatility assumptions carry over, and the Monte Carlo monthly rate from step 1 becomes your contribution. Add your ages and planned retirement spending: 5,000 simulated market paths show the probability your money lasts as long as you do.
Check your inputs.
Challenge the plan against history
Monte Carlo draws random futures from a statistical model. The World Simulator does the opposite: it replays your plan through more than a century of actual market history — booms, crashes, and long sideways decades included — so you can see how it would have fared in the worst starting years on record.
Frequently asked questions
Why do the two steps give different monthly numbers?+
Step 1 solves a simpler problem: reach a fixed target by a fixed date. Step 2 simulates the whole plan including the withdrawal phase, where the sequence of market returns matters enormously — a crash early in retirement hurts far more than the same crash later. It is normal for a plan that hits its accumulation target to show less than 100% success once withdrawals are simulated.
What do “real returns” and “today's dollars” mean?+
Both calculators work in inflation-adjusted terms: the returns you enter should be net of inflation (for example, roughly 5% real for a diversified stock portfolio historically, versus 7-10% nominal), and every dollar figure you see is in today's purchasing power. That way you never have to guess what a number will feel like decades from now.
Is a 90% success probability good enough?+
There is no universal threshold. A 90% success rate means roughly 1 in 10 simulated futures ran out of money before the plan's end age — but real people adjust: they spend less in bad years, work a little longer, or annuitize. Treat the probability as a way to compare plans, not a guarantee. These simulations are educational tools, not financial advice; for a decision this large, a fiduciary advisor can weigh factors no calculator sees.
Are my inputs stored or sent to a server?+
No. Both simulations run entirely in your browser with a fixed random seed, so identical inputs always reproduce identical results and nothing you enter leaves your device.