Methodology

Net worth

Net worth is the sum of the converted value of every asset you have entered, in your chosen display currency. For each asset:

• Stocks, cryptocurrency, and precious metals: price × quantity, where price comes from Yahoo Finance.
• Real estate and vehicles: manualPrice × quantity − mortgage (the loan balance is subtracted).
• Cash and retirement: manualPrice (a single balance you maintain).
• Other: manualPrice × quantity.

The result is converted from each asset's native currency into your display currency using the FX rate described below.

Live prices

Stock, cryptocurrency, and precious-metal prices are fetched from Yahoo Finance via the yahoo-finance2 library. Prices are cached in-memory for 10 minutes and shared across all users on a server instance — this keeps quotes fresh while staying within Yahoo's public rate limits.

Real-time prices may be up to 10 minutes delayed. Manual-price asset types (real estate, vehicles, cash, retirement, other) update only when you edit them.

FX conversion

Exchange rates are pulled from Yahoo Finance using the standard pair format (USDCNY=X, EURUSD=X, and so on). Rates are cached for 24 hours.

Prism supports eight currencies natively: USD, CNY, AUD, EUR, GBP, JPY, CAD, and HKD. Each asset is stored in its own currency in the database. Conversion to your display currency happens at read time, never at write time, so changing the display currency never alters your underlying data.

FIRE Number (the 4% rule)

The FI Number — the portfolio size at which work becomes optional — is calculated using the Trinity Study 4% safe withdrawal rate:

FI Number = monthly expenses × 12 × 25

The Trinity Study (Cooley, Hubbard, Walz, 1998) found that a 4% inflation-adjusted annual withdrawal rate had a high probability of sustaining a 30-year retirement on a 50/50 stock/bond portfolio. Multiplying annual expenses by 25 (the inverse of 4%) gives the target portfolio size. Like all rules of thumb, it's a planning anchor, not a guarantee.

Years to FI

Given your current net worth (NW), monthly savings (S), and expected real annual return (r), Years to FI is the closed-form solution to the future-value equation:

years = log((FI · r + 12·S) / (NW · r + 12·S)) / log(1 + r)

This assumes constant real returns and constant real contributions — a simplification. Real markets vary; sequence-of-returns risk matters. Use this as a directional estimate, not a forecast.

FIRE milestones

• Lean FI — 60% of FI Number; basic-needs financial independence.
• Regular FI — 100% of FI Number; full Trinity 4% rule.
• Fat FI — 150% of FI Number; comfortable buffer above the 4% rule.
• Coast FI — the portfolio size today that, with no further contributions, compounds to the FI Number by your target retirement age. Formula: FI Number / (1 + r)(targetAge − currentAge).

Snapshots

Prism records a daily net-worth snapshot at midnight UTC via a Vercel Cron job, plus an automatic snapshot every time you create, edit, or delete an asset. Snapshots are grouped by asset type so the dashboard chart can show how each category contributes to net worth over time. Snapshots survive asset deletion via denormalized userId and assetTypefields, so historical totals stay accurate even after you remove an asset.

What Prism does not do

• No bank, brokerage, or Open Banking integrations. No Plaid, no Yodlee.
• No tax reporting, capital-gains tracking, or dividend reinvestment modelling.
• No automated transaction import — every position is entered or edited by you.
• No Monte Carlo simulation or sequence-of-returns modelling. Years to FI is deterministic.

Prism is a tracker and a planner, not a financial advisor. Numbers shown are informational; verify with a qualified professional before making consequential decisions.