FREE · 10,000-PATH MONTE CARLO · 2026 DATA
Retirement calculator
Five inputs, a real 10,000-path Monte Carlo, and the 2026 federal rules baked in.
Yearfold is a financial-education tool. It is not a registered investment adviser and does not provide personalized investment, tax, or legal advice. Results are probabilistic projections based on historical data and stated assumptions; they are not guarantees. Methodology
STEP 1 OF 3 · YOUR BASICS
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What this calculator does
A free, browser-first retirement calculator that runs a real 10,000-path Monte Carlo simulation against 2026 federal rules. It models couples as two earners with two Social Security claim ages, models dependents as period-bounded costs, and applies the post-OBBBA tax brackets, the over-65 standard deduction, Social Security taxability (still frozen at the 1983/1993 thresholds), the Medicare Part B base premium with IRMAA tiers, and SECURE 2.0 RMDs.
What you get back: a success probability (the share of the 10,000 simulated futures where your money lasts your full horizon), a fan chart of the 10th / 50th / 90th percentile balance trajectories year by year, and three ranked shortfall fixes (“contribute $340 more/month or retire 14 months later or claim Social Security at 70”) sorted by how much they move the success probability per unit of effort.
What you'll need to fill in
Your current age, your total invested balance (IRAs, 401(k)s, taxable brokerage), your monthly contribution, your target retirement age, and your expected monthly spending in retirement in today’s dollars. If you’re a couple, add your spouse’s age and retirement target. Optional fields — Social Security PIA, asset allocation, claim age — refine the answer; the defaults are sensible if you’d rather skip them.
About two minutes for a first pass. The simulation itself runs in your browser in under a second on a typical laptop and a few seconds on mid-range mobile. Nothing is sent to our servers — your inputs stay in your browser unless you choose to save a plan.
How this works under the hood
A Monte Carlo simulation is the opposite of the “assume 7% per year forever” straight-line projection most calculators use. Instead, ten thousand parallel futures get rolled forward, each one a different plausible sequence of market returns and inflation drawn from real monthly history. Some of those futures look like 1929 or 2000 at the start of retirement — bad sequence-of-returns risk — and some look like 1982 or 2009 — great timing. The point is to see the distributionof outcomes, not a single line.
On top of that simulation, Yearfold layers the 2026 federal rules that actually determine how much of each year’s gross withdrawal you keep: tax brackets, standard deduction, Social Security taxation, IRMAA tiers, RMDs. Every assumption and data source is documented and cited.