Retirement Is a Set of Choices, not a fixed calculation.

Each simulation is stitched together from real stretches of US market history from 1953 to 2025: stock returns, 10-year Treasury returns, Treasury bill rates and inflation, all taken from the same months. Thousands of these simulations are run, and the success rate is the share in which your money lasts as long as you need it.

Enter the benefit at full retirement age from your statement at ssa.gov and pick a claiming age from 62 to 70. The calculator applies the Social Security Administration's early-claiming reductions and delayed retirement credits, adds a spousal benefit when half of a spouse's benefit is larger than a person's own, and raises benefits with inflation.

Claiming at 62 pays 70% of your full benefit for longer; waiting until 70 pays 124% for a shorter time. Which is better depends on how long you live, your other savings and your spouse. After you run a plan, the What You Control section tests every claiming age against the same simulated markets and shows how much you could sustainably spend with each.

Withdrawals are grossed up by a flat effective tax rate, which you can estimate from your mix of traditional, Roth and taxable accounts. Annual fund and advisory fees are charged on invested money. Inflation is replayed from history by default, so periods like the 1970s raise spending as they actually did.

They replay your retirement through what really happened if you had retired at famous moments, such as 1929 (the Great Depression), 1966 (stagflation), 1973, 2000, October 2007, and 2022, using that era's actual returns and inflation. The 1929 and 1937 tests use data from before 1953, which the simulations don't sample. Two more drop the Great Depression on the five years before you retire, with and without a job loss. They also check every possible retirement start month since 1953 and report how many your plan would have survived. A set of life events shows how your success rate changes if Social Security is cut, you have to retire early, you need years of long-term care, or you live to 100.

FIRECalc and cFIREsim replay each actual 30-year period in history and count how many lasted. This calculator shuffles real 5-year stretches of 1953-2025 history into thousands of new sequences. At a 4% withdrawal rate the two methods mostly agree. At higher rates the simulations here tend to come out higher: for $1 million, $50,000 a year, 30 years, and 60% stocks, about 78% here versus 61% to 69% in FIRECalc. Replaying actual periods keeps long bad stretches like 1966-1982 intact and counts them many times. The simulations weight every year equally, including 2000-2025, and can show bad sequences that never happened. Neither method is more correct. For the replay answer, open the historical stress tests, which check every start date since 1953 the same way (63% for that example). When the two disagree, the lower number is the cautious one.

Coast FIRE means you have saved enough that, with no further contributions, your investments should grow to cover retirement by your target retirement age. You keep working to pay your current bills, but you stop saving for retirement and let growth carry you there. This calculator finds the earliest age you could stop saving at each success rate.

A cash buffer holds a few years of withdrawals in Treasury bills. When the market is more than 10% below its peak, spending comes from the buffer instead of selling investments at a loss, and the buffer is refilled after the market recovers. The calculator shows how often the buffer carried you through a downturn and how often it ran out.

No. Everything runs in your browser and nothing you enter is sent to a server. There is no sign-up. If you copy a link to a plan, the plan's numbers are carried inside the link itself, so anyone you send it to can see them.

No. PortfolioSim is for information and education only. It is not financial, investment, tax or legal advice, it doesn't know your full situation, and nothing on it is a recommendation. Results are hypothetical, based on historical data, and the future may differ from the past. Talk with a qualified professional before making financial decisions.