How It Works — Methodology, Assumptions & Privacy

Nothing here is a black box. This page is the whole model: what we compute, what we assume, what we deliberately leave out, and what happens to your data (short version: it stays with you).

Model version 4.1 · Updated 2026-07 · IRS limits and defaults reviewed for 2026

The words on your plan

Work-change age (formerly Pivot Date): The earliest age you could change how you work — retire, go part-time, switch careers — with the plan staying funded through your life expectancy, given the earned income you expect after the change.
Full FI age: The earliest age your investments (plus non-earned income like Social Security or a pension) could support your spending with no earned income at all. If your bridge income never materializes, this is your backstop.
Bridge Income: The minimum earned income you'd need after your work change for the plan to hold at your chosen age. It bridges the years between the pivot and full financial independence.
Safety Margin: How the plan holds up when assumptions get worse. Strong: funded even in the conservative case. Moderate: funded on base assumptions. Thin: only funded if markets outperform. Short: not funded even optimistically.
Coast Point: The first date your invested balance alone — with zero further contributions — would compound to your FI number by your target age. Past it, contributions are optional.
FI Number: The portfolio size where a safe withdrawal covers your net spending: net monthly spending × 12 × (100 ÷ withdrawal rate). At the default 4%, that's 25× net annual spending, inflated to your change date.
Savings rate: WorthCurve reports your FI investment rate: monthly contributions to invested accounts (including employer match) divided by monthly take-home income plus match. Cash set aside but not invested isn't counted — it doesn't compound toward FI.

The simulation

Everything runs on one month-by-month simulation from today to your life expectancy — the planner, the comparison table, and the calculators all share it, along with one set of assumptions. When two numbers differ on this site, it's because the decisions differ, never the model.

Growth.Invested balances compound monthly at your assumed annual return (default 7% nominal). Cash doesn't grow — which is why the “in vs. growth” view is worth a look.
Inflation.Applied monthly to income, expenses, and inflation-adjusted income streams (default 3%/yr), so far-future dollars aren't flattered.
Debts. Each debt accrues its own interest monthly; payments follow your chosen strategy (avalanche = highest rate first, snowball = smallest balance first).
Future income streams. Social Security, pensions, rentals, and part-time income each have an amount, start age, optional end age, and an inflation flag. They flow into both the saving years and the drawdown years.
After the change. At your work-change age, earned income switches to your bridge income (zero for a full stop), spending switches to your after-change budget, contributions stop, and shortfalls draw down cash first, then investments — until the money runs out or outlasts the plan. That drawdown, not a rule of thumb, drives every verdict.
Solved dates, not sliders. Your work-change age and full FI age are found by searching the simulation for the earliest whole-year age that stays funded to your life expectancy. Bridge Income is found the same way, over income instead of age.
Invested assets, not net worth. Projections run on money that can actually fund spending: invested accounts plus cash. Home equity, vehicles, and 529 balances are tracked but never assumed to pay your bills.
Contribution limits. The checkup uses the 2026 IRS limits ($24,500 employee 401(k); $7,500 IRA shared across Roth and Traditional; $4,400 / $8,750 HSA self / family) and models employer match as match-rate × contribution, capped at a share of salary.

How uncertainty is shown

One deterministic line pretending to be the future is the most common lie in retirement software. WorthCurve runs every plan three times:

Conservative: your return −2 points, inflation +0.5.
Base: your assumptions as set (default 7% return, 3% inflation).
Optimistic: your return +2 points, inflation −0.5.

The band on every chart is the spread between conservative and optimistic; the safety margin summarizes which of the three cases actually stay funded. It's deliberately simpler than a Monte Carlo simulation — visible uncertainty you can reason about, not a probability cloud that invites false confidence in a different way.

Deliberately not modeled

Each of these adds assumptions that would create precision the inputs can't support. Leaving them out keeps one legible model so you can compare decisions on equal footing — and each omission has a cost worth knowing about:

taxes on withdrawals. A dollar in a pre-tax 401(k) buys less spending than a dollar in a Roth. Treating them equally flatters plans that are heavy in pre-tax balances.
sequence-of-returns risk. A bad early decade of returns can deplete a withdrawal portfolio faster than any long-run average suggests. The conservative band lowers the average; it does not simulate ordering.
healthcare costs as a separate spending category. Healthcare costs often grow faster than general inflation and dominate early-retirement budgets before Medicare.
Roth conversion ladders and other early-access strategies. Strategies like Roth conversion ladders, SEPP/72(t), and the rule of 55 change when money is accessible, not how much there is.
state-specific taxes and rules. State income tax, property tax, and benefit rules vary enough to shift a marginal plan either way.

Review these against your own situation before relying on a result, and verify the details with a financial or tax professional when a decision gets real. WorthCurve is an educational tool, not financial advice.

Where your data lives

On your device.Plans are computed and stored in your browser's local storage. There are no accounts and no server-side copies.
Share links.Created only when you click “copy share link”. The plan travels in the URL fragment(after the #), which browsers never send to servers, referrer headers, or analytics. Anyone you give the link can see those numbers — that's the point — so share deliberately.
Analytics.Anonymous interaction events only (“plan started”, “chart toggled”). Your financial values are never sent — and because plan state never appears in the page URL, they can't leak through page-view tracking either.
Deleting.“Delete all my data” in the plan's share menu erases every WorthCurve key from your browser. Export a .worthcurve file first if you want a backup — it's yours, readable JSON.

Full privacy policy →

Model changelog

v4.1 2026-07
Employer match is now pro-rated by the share of your own contribution the month's cash flow actually funds, instead of accruing in full even in months you couldn't contribute. Plans that are never cash-constrained are unchanged; cash-constrained plans now show slightly lower invested balances.
v4.0 2026-07
Personalized plans built from life goals. Added future income streams (Social Security, pensions, part-time, rental), conservative/base/optimistic bands on every chart, solved Pivot/Full-FI dates and Bridge Income, safety margins, and a path comparison workspace. Share links moved to URL fragments; one-click delete-all-data control.
v3.x 2026-06
Account buckets (401(k), Roth IRA, HSA, 529, brokerage, cash) with employer match and IRS limits; contribution checkup; Coast FI; FI path presets.
v2.x 2026-05
Freedom goal with post-FI drawdown simulation; debts with avalanche/snowball payoff; scenario branches.

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