Methodology & Sources
Every number, and where it comes from.
A money tool you can't audit is worthless. Here is exactly how TrueWorth computes what it shows — and exactly where it makes assumptions.
Inflation — the spine of everything
Almost everything TrueWorth shows runs on one number: the Consumer Price Index for All Urban Consumers (CPI-U), BLS series CPIAUCNS, base 1982–84 = 100, published by the U.S. Bureau of Labor Statistics. We source it via the open datasets/cpi-us project and store it in /data/cpi-u-annual.json as annual averages from 1913 through 2025, with the latest monthly print (April 2026) carried in as the "today" reference.
There is exactly one identity behind both Real Salary and Life of a Dollar:
value in year B = nominal × CPI(B) ÷ CPI(A)
That's it. No black box. The annual averages we ship are cross-checked against the underlying monthly series, so a number you see in TrueWorth is a number you could rebuild yourself from BLS data in a spreadsheet.
Investment returns — clearly an assumption
The Opportunity Mirror compares your purchase against asset classes using long-run average nominal returns. These are applied as assumptions — not a backtest of your specific years, and not a promise:
S&P 500 stocks ≈ 10%/yr — total return, dividends reinvested; the long-run historical average.
Gold ≈ 7%/yr — long-run, and highly era-dependent.
Investment-grade bonds ≈ 5%/yr.
Cash 0% — it just sits there.
Real markets are volatile and path-dependent — the order in which gains and losses arrive matters enormously. A flat average is a teaching device, not a forecast. These figures reflect widely-published long-run studies of U.S. asset returns; your actual outcome over any specific window could be very different.
Cash erosion — this part is exact
The "cash's real value today" figure is computed straight from CPI-U, with no assumption at all. It's the same inflation identity above, applied to idle cash — showing how much purchasing power money quietly lost just by sitting still. When the Opportunity Mirror tells you what your cash is really worth now, that number is as solid as the inflation data itself.
Resale / depreciation — rough estimates
When TrueWorth estimates what an item you bought is worth today, it uses simple per-category annual depreciation curves with a floor. Phones and electronics fall fast; cars depreciate more slowly; luxury goods slowest of all. These are directional estimates, not an appraisal — useful for seeing the shape of the loss, not for setting a resale price.
Historical price anchors — approximate, sourced
The "what a dollar bought" prices in Life of a Dollar are rounded, widely-cited figures pulled from public sources: the U.S. Bureau of Labor Statistics, the U.S. Census Bureau, the U.S. Department of Education, the U.S. Postal Service, the U.S. Energy Information Administration (EIA), and NADA / Kelley Blue Book. They illustrate scale and direction — how far a dollar reached then versus now — not exact receipts.
What we don't do
No accounts. No tracking. No servers ever see your numbers. No ads. No affiliate links. Nothing sold. Everything runs in your browser — the math happens on your device and stays there. And it's open source: you don't have to take any of this on faith. Read every line on GitHub and check the work yourself.
TrueWorth is not financial, investment, or tax advice. It shows what your money is doing; it does not tell you what to do with it.