📊Monte Carlo Retirement Calculator

Why Monte Carlo Beats Fixed-Return Assumptions

Most retirement calculators assume a fixed annual return – say 7% per year. But real markets don't deliver smooth returns. The S&P 500 has experienced annual losses exceeding 30% multiple times (2008, 2020, 2022). Monte Carlo simulation runs your retirement plan through 10,000 different market paths, each with realistic sequences of gains and losses drawn from historical US market data. This reveals the range of outcomes you might actually face – from 'never run out of money' to 'depleted by age 78' – giving you a probability-based view rather than a false sense of certainty.

Vanguard – Retirement Planning Research

Sequence of Returns Risk Explained

A retiree who experiences a bear market in the first 3-5 years of retirement faces dramatically worse outcomes than one who experiences the same bear market 15 years in. This 'sequence of returns risk' is invisible in average-return calculations but is the primary destroyer of retirement portfolios. Our Monte Carlo simulator specifically tests for this by varying when market crashes occur across 10,000 scenarios. If your portfolio survives the worst sequences, you can retire with high confidence.

Journal of Financial Planning – Sequence Risk Studies

The 4% Rule and Its Limitations

The famous '4% rule' – withdraw 4% of your portfolio in year one, then adjust for inflation – was derived from historical US data by William Bengen in 1994. While useful as a starting point, it has significant limitations: it assumes a 30-year retirement (problematic for early retirees), uses only US historical returns (which may not repeat), and doesn't account for Social Security timing or variable spending. Monte Carlo simulation improves on the 4% rule by testing dynamic withdrawal strategies across thousands of market environments, often revealing that 3.5% is safer for early retirees while 4.5% may be fine for those with guaranteed Social Security income.

Financial Analysts Journal – Safe Withdrawal Rates

What success rate should I target?

Most financial planners recommend a Monte Carlo success rate of 85-95%. A 90% success rate means that in 9,000 out of 10,000 simulated market scenarios, your money lasted through retirement. Going above 95% often requires excessive savings that reduce quality of life during working years. Below 80% suggests meaningful risk of running out of money. If your result falls below 85%, consider working 1-2 more years, reducing planned spending by 10-15%, or delaying Social Security to age 70 for a higher guaranteed benefit.

How does Social Security affect my simulation?

Social Security acts as a powerful stabiliser in Monte Carlo simulations because it provides inflation-adjusted guaranteed income regardless of market performance. Delaying Social Security from age 62 to 70 increases your monthly benefit by approximately 77%. In our simulations, this delay typically improves success rates by 5-15 percentage points because the higher guaranteed income reduces the amount you must withdraw from your portfolio during market downturns – precisely when withdrawals are most destructive.

Should I include my home equity in the simulation?

Generally, no – unless you plan to downsize or use a reverse mortgage. Home equity is illiquid and doesn't generate cash flow for living expenses. Our simulator focuses on investable assets: 401(k), IRA, Roth IRA, taxable brokerage accounts, and cash. If you do plan to sell your home and downsize, you can model the net proceeds as a lump-sum addition to your portfolio at the planned sale date.