Guide
Will my money last in retirement?
It's the question every plan is really asking. A trustworthy answer needs two things: a full projection, and a probability — not a rule of thumb.
Updated July 11, 2026
Why a single number can't answer it
“Will my money last” depends on how markets behave over decades you can't predict. A single projected balance assumes one fixed return every year, which never happens — the order of good and bad years matters as much as the average.
That's why serious planners report a probability instead: run the plan across many possible market paths and count how often the money survives to the end.
What a Monte Carlo simulation tells you
A Monte Carlo simulation runs your exact plan hundreds or thousands of times over randomly sampled return sequences. If the money lasts in, say, 850 of 1,000 runs, your plan's success probability is about 85%.
It's not a guarantee — it's a calibrated sense of how much margin you have. A 95% plan is sturdy; a 70% plan is telling you to adjust spending, work a little longer, or claim Social Security differently.
The details that quietly move the answer
Taxes, required minimum distributions, and how Social Security is taxed all change how long your money lasts — and they interact. A withdrawal from a traditional account can push more of your Social Security into taxable territory, which raises the withdrawal you need, and so on.
Meridary models those interactions year by year so the probability reflects your real after-tax cash flow, not a pre-tax approximation.
Related free calculators
Frequently asked
- What is a good probability that my money will last?
- Many planners treat roughly 85–95% as a comfortable range. Below that, small changes — spending, retirement date, Social Security timing — can meaningfully improve the odds.
- Is a Monte Carlo result a guarantee?
- No. It's an estimate of how often your plan survives across many simulated market paths. It quantifies uncertainty; it doesn't remove it.