Blog
Deep dives into Monte Carlo simulations, retirement risk, and the math behind your plan.
How Much Do I Need to Retire? Savings by Spending and Age
The savings you need on the day you retire, by monthly spending, pension, retirement age and how sure you want to be, from 10,000 simulated futures.
When Can I Retire? Find Your Earliest Retirement Age
Your chance of the money lasting for every retirement age, from your savings, monthly saving, spending and pension, run through 10,000 simulated futures.
Best Retirement Calculators 2026: 6 Tools Compared
Six retirement calculators compared from their own websites: what each costs, how it simulates, how it handles taxes, and which question it answers best.
Guardrails vs the 4% Rule: How Much More Can You Spend?
Guyton-Klinger guardrails let you start spending much more than the 4% rule. Here is what you get to spend 10 and 20 years later, from 10,000 simulated futures.
What Is a Good Monte Carlo Success Rate for Retirement?
70%, 90% or 99%? Every extra point of safety costs monthly spending. See the price of each target and what the failed futures look like.
4% Rule Calculator: How Often Does 4% Really Last?
Test the 4% rule against 10,000 simulated futures: pick your withdrawal rate, how long it has to last, the market outlook and your stock share.
Can I Retire at 55? What Each Extra Year of Work Buys
Retiring at 55 means fewer years of saving, more years of withdrawals and a long wait for a pension. See what each extra year of work changes.
How Long Will 1 Million Last in Retirement?
It depends on what you spend and what other income you have. We ran 1 million through 10,000 simulated futures for every combination - try yours.
How to Choose a Retirement Spending Strategy: A Decision Framework
Most retirees drift into the wrong spending strategy by default. A four-input decision framework picks the right one and rules out the costly mismatches.
Reading a Monte Carlo Success Rate: Why 90% Is Not What You Think
The success rate is a useful summary, not the answer. A complete reading uses the failure distribution, worst-case income, and assumption sensitivity together.
The Endowment Approach to Retirement: Percentage-of-Portfolio Withdrawals
University endowments solved sustainable spending decades ago: take a percentage of the portfolio, smooth it. Same approach works for retirees with the right income structure.
What Expected Return Should You Use in a Monte Carlo Retirement Plan?
The assumed return is one of the most powerful inputs in a retirement simulation - and one of the least certain. How to choose it, and why to test more than one.
Floor and Ceiling Withdrawals: When Income Bounds Hold and When They Break
A floor protects your income; a ceiling protects your savings. How the strategy works, where the risk sits, and when it is the right fit.
How to Model Social Security in a Monte Carlo Retirement Plan
Social Security is the most stable income in many retirement plans, but it is easy to model too simply. Claiming age, adjustments and survivor benefits, explained.
Guyton-Klinger Guardrails: Spending That Bends Instead of Breaking
The 4% rule ignores markets. Guardrails cut spending after bad years and raise it after good ones. How the rules work, and how to choose the settings.
European Retirement Planning: Why the 4% Rule Is American
Bengen's 4% rule was derived from US history. International research shows safe withdrawal rates are materially lower in most European countries.
Black Swan Events: The Crash Your Retirement Plan Is Hiding
A bell curve treats a year like 2008 as a once-in-centuries event, yet U.S. stocks have had several. How to test your plan against a crash at the worst time.
Do Bonds Really Protect You When Stocks Crash?
In 2008, bonds gained 20% while stocks fell 37%. In 2022, both fell 18%. How often bonds really cushion a crash - and how a simulator should model it.
What Is a Monte Carlo Retirement Calculator?
How Monte Carlo retirement calculators work, why they beat fixed-return projections, and what separates a good one from a basic spreadsheet.
Variance Drain: The Silent Killer of Retirement Portfolios
Gain 20%, lose 20%, and you are down 4%. Variance drain silently erodes compound growth by 1-2% per year, and it gets worse under fat tails.
Monte Carlo vs Historical Backtesting: Which One Should You Trust?
Historical backtesting tests your plan against the past. Monte Carlo tests it against everything that could happen. You need both.
Why Average Returns Lie: Geometric vs Arithmetic
Your advisor says 8% average return. Your account grew at 6.7%. The gap is variance drain, and over 30 years it adds up to a large share of your savings.
The 4% Rule Is Not a Rule
The 4% rule is not a law of physics. It is a historical observation about one country during one era, applied to a strategy most people should not use.
Four Retirement Spending Strategies, Ranked by Survival Rate
Same savings, same returns, different spending rule. Four strategies compared on how long the money lasts and what you actually get to spend.
How Many Iterations Does a Monte Carlo Simulation Need?
Run the same simulation twice, get a different answer. If your Monte Carlo success rate bounces around, you do not have enough iterations.
Fat Tails and Retirement: How Often Do Big Crashes Really Happen?
The S&P 500 lost 30% or more in three calendar years since 1928 - about twice what a bell curve expects. What that means for a retirement plan.
Why the Order of Your Returns Matters More Than the Average
Two retirees, same average return, opposite outcomes. Sequence-of-returns risk is one of the biggest risks in retirement - and one a simple calculator cannot show.