RetireSimulator

Five steps, one simulation engine, entirely local to your browser

Retirement Simulator is a free, browser-based Monte Carlo retirement calculator and planner available on its own domain. The tool takes a five-step approach to retirement planning: establish your timeline, project your net worth, model lifetime income and expenses, then test how the balance pays out across four different withdrawal methods. Every calculation runs locally on your device. Your data never leaves your browser. There are no accounts, no servers, no persistent storage beyond your own local device storage. The plan is stored only in browser local storage on the device, and clearing your browser's site data erases the plan entirely. This is a deliberate design choice, traded off against the convenience of synced accounts: you own your data completely, and the tool makes no attempt to keep anything about you.

Assets by category, income by earner, expenses with optional smile curve

The income layer starts with your timeline: your current age, your planned retirement age, and optional spouse ages on one household axis. Everything else hangs off this line. Then you model net worth by recording present resources in broad asset classes (cash, investments, retirement accounts, real estate, business, other) minus mortgages and liens. Approximate figures are sufficient, though greater precision can be added wherever wanted. Income is projected year by year with no randomness (that is the deterministic part). You enter salaries with raises to each earner's retirement, and Social Security is auto-placed at the claim age you choose. The site describes this as the U.S. Department of Labor's planning sequence. Everything saves automatically on the device, so a change to expenses is reflected in the income, expenses, and spend-down steps together. Expenses can be entered as a monthly headline number or broken down by category. You can optionally model a retiree smile curve, the pattern where spending is high in early retirement (travel and hobbies), dips in the middle years, and rises again in late life (healthcare). You can also model a mortgage payoff on a schedule you set. Required withdrawals are estimated from age 73 (RMD Estimator available separately as a reference tool).

Four withdrawal methods, mortality-weighted lifespans, percentile outcomes

The spend-down calculation is where the Monte Carlo runs. The tool simulates your plan year by year across thousands of modeled and historical market paths. The simulation engine is the same for all methods. Historical markets replay rolling 1928–2024 windows, providing real-world sequence-of-returns risk instead of average returns. The tool also models markets with a lognormal distribution (theoretical random walks). Each scenario draws lifespans from a simplified mortality table, so the horizon ends at the second death for couples. That approach (mortality-weighted horizons) reflects that outliving money is measured across scenarios, not assumed away with a fixed death date. Four withdrawal families are tested: Steady (constant-dollar amounts year to year), Flexible (constant percentage of portfolio), Spend-All (amortized VPW or ABW with growth tilt), and Guardrails (simplified Guyton-Klinger, the academic best-practice strategy). The tool runs the same simulation engine for every method, so you see which strategy works best for your specific numbers. Paths are summarized as percentile bands: the P10 (bad-luck outcome), the median outcome, and the good-luck outcome. The site describes Steady as viable when the bad-luck (P10) ending clears the buffer; adaptive methods are viable when worst-year P10 income covers essentials.

Free, entirely, with a donation option

Retirement Simulator is free. No cost, no accounts, no paywall. The site states this explicitly and describes itself as a free, no accounts, no paywall project. The only monetization is a "Buy me a coffee" donation link, a voluntary option for users who found the tool helpful and want to support its continued existence. No subscription, no pricing tiers, no limited features. The perpetual trade-off is the entirely local computation: your data never syncs across devices, so if you switch browsers or computers you start over. You can export scenarios to CSV for backup or for sharing with a CFP, but there is no cloud storage or automatic backup. Everything you enter stays on the device you entered it on. The tool makes this design choice deliberately: it prioritizes privacy over convenience.

Who it suits; what it is not built for

Retirement Simulator suits the planner who wants to run multiple scenarios quickly on their own device and understands that local storage is the trade-off for full privacy. The historical market replay (1928–2024 windows) appeals to anyone who wants to stress-test against real sequences of returns, not theoretical averages. The four withdrawal methods (especially Guardrails, the Guyton-Klinger adaptive strategy) appeal to the FIRE community and to the self-directed planner who reads academic research. The free price removes friction entirely. A real limitation is that all computation is local on your device, so calculations can be slower on older hardware for very long horizons or complex scenarios. The tool does not connect to your accounts, so precision depends entirely on the numbers you enter. It does not handle outside-the-USA scenarios in the interface, though the mortality table and the math are general. For someone who changes devices often or wants their plan accessible on the phone and the laptop and the home computer at the same time, the local-only storage is a dealbreaker. For someone who wants to see the full working behind every number, export a scenario to show a CFP, and have complete privacy from any server, this is exactly the design. The site is explicit about what it is: "This is a simulation tool for informational and educational purposes only. It does not constitute financial advice. Results depend on the assumptions and inputs provided and do not guarantee future outcomes."

Reference tools for verification

The tool includes reference calculators you can use independently or to sanity-check your inputs: a Wealth Ladder to understand withdrawal sequencing by account type, Key Ages (a guide to major retirement milestones), an RMD Estimator to project required minimum withdrawals from age 73 onward, Tax Tables as a reference, and a Mortgage Payoff calculator. These are not integrated into the main simulation, but they are available for verification. The dashboard synthesizes the five steps into one verdict: based on all the numbers you entered and the four withdrawal methods tested, is your plan feasible under at least one method? When nothing is viable, the dashboard prescribes one change at a time (the earliest retirement age that works, or the smallest increase in extra savings) and names which method it unlocks. Every assumption is listed, failures are histogrammed by age, and a no-luck projection reconciles against the stochastic median as a standing self-check. You can replay three scenarios (bad-luck, median, good-luck) year by year and export them to CSV for audit or for sharing.