What is a Monte Carlo retirement simulation?

A Monte Carlo retirement simulation runs many possible market-return paths instead of assuming one steady return every year. It estimates how often your portfolio lasts through retirement under those random return paths.

What success probability should I target?

Many planners treat 80% to 90% as a useful planning range, but the right target depends on flexibility, guaranteed income, risk tolerance, taxes, health, and whether you can reduce spending during poor markets.

Does this calculator include Social Security or taxes?

This version models portfolio savings, contributions, inflation, withdrawals, average returns, and volatility. It does not separately model Social Security, pensions, tax brackets, required minimum distributions, or account-specific tax treatment.

Why can Monte Carlo results change from simple retirement calculators?

A simple calculator often assumes the same return every year. Monte Carlo simulations include bad early-return sequences, good markets, flat periods, and compounding differences, so they expose sequence-of-returns risk.

Retirement Monte Carlo Calculator

Runs locally in your browser No signup Inputs stay private Educational estimate only

A straight-line retirement calculator hides one of the biggest risks: bad returns early in retirement. This calculator uses a seeded Monte Carlo model so the same inputs produce the same shareable result, while still testing thousands of possible market paths.

Your retirement assumptions

Current age

Retirement age

Plan through age

Simulations

Current retirement savings

Annual contribution until retirement

Annual retirement spending today

Annual Social Security/pension income today

Optional one-time retirement expense

Expected annual return

Annual volatility

Annual inflation

Annual fees/tax drag

Scenario seed

This calculator is for education, not personalized investment advice. It uses simplified inflation-adjusted Social Security or pension income if entered, but it does not model benefit claiming rules, taxes, account type rules, healthcare shocks, or advisor recommendations. Read the disclosure.

Estimated success probability

Median ending balance--

10th percentile--

90th percentile--

Median depletion age--

Your next move

Outcome range

These balances are after the final planned year. The 10th percentile is the rough downside case; the 90th percentile is a strong-market case.

10th percentile

Median

90th percentile

Simulation paths

Each line is one simulated portfolio path from your current age through the final planned age. Colors are assigned deterministically from the run number, so the same inputs and seed draw the same chart.

AgePortfolio balance

What to try next

What-if comparison

These use the same seed so the differences come from the changed assumption, not a different random draw.

Scenario	Success probability	Median ending balance	Change

Projection snapshots

Age	Median balance	Downside balance	Strong-market balance

How this calculator works

Each simulation year draws a random return from a normal distribution using your expected return and volatility assumptions. Before retirement, the calculator compounds savings and adds annual contributions. At retirement, it inflates your spending target from today into retirement dollars, then withdraws that amount each year while continuing to apply random returns.

A run counts as successful if the portfolio never hits zero before the final planned age. Ending balances are shown as percentiles across all simulation runs. Negative balances are treated as zero after depletion.