Data Sources & Methodology

Last updated: 2026-08-12

FomoDejavu uses historical datasets and scenario-based calculations for educational purposes. This page describes how the current calculator stack handles source data, dates, dividends, inflation, rounding, and known limitations. It documents existing behavior and does not change the calculation engine.

Data sources and coverage

Stocks and ETFs

Historical market prices and dividend events are served from the application's local Parquet-backed market dataset. Coverage is instrument-specific, so each ticker can have a different earliest and latest available date.

Cryptocurrencies

Cryptocurrency price history is read from the local crypto dataset through the application's DuckDB-backed data service. Crypto calculations do not add stock dividends or stock-split events.

Benchmarks

S&P 500, Nasdaq, gold, and silver comparison series are read from local benchmark datasets. Benchmark availability can differ from the selected asset's coverage.

Inflation

Optional inflation-adjusted outputs use the CPI series packaged with the application. Inflation coverage and update timing can differ from market-price coverage.

There is no single universal market-data cutoff for every asset. The calculator uses the observations actually available for the selected instrument and date range.

How calculations work

Simple Growth

Simple Growth uses the first and last available stored closing prices in the resolved date range. Shares are calculated from the initial investment and the starting close, and final value is based on those shares multiplied by the ending close. This mode does not add separate dividend cash flows.

Dividend Investor

Dividend Investor uses recorded dividend events for the selected instrument. Each dividend payment is calculated from the shares held at that point and is reinvested using the recorded reinvestment price, which can add fractional shares. Those additional shares participate in later dividend payments.

Splits and corporate actions

Calculations use historical prices and events as stored in the configured datasets. Source normalization can reflect corporate actions in the stored series, but the calculator does not independently reconstruct or guarantee complete treatment of every historical merger, spin-off, delisting, symbol change, or other corporate action unless that treatment is explicitly represented in the underlying data.

Unavailable and non-trading dates

The calculator does not invent a market price for a date with no observation. A requested start date is resolved to the first available observation in the permitted range, and the calculation end resolves to the last available observation in the range. If a requested end date extends beyond current available market data, it can be capped to the latest permitted date. The result indicates when dates were adjusted.

Recurring contributions

Where monthly recurring contributions are enabled for Simple Growth, contributions after the starting month are applied using the first available price observation for each later month. Recurring contributions are not currently applied to Dividend Investor mode.

Inflation adjustment

When inflation adjustment is selected, the calculator compares CPI observations for the start and end months and converts supported outputs into estimated real purchasing-power terms. If an exact CPI month is unavailable, the data layer can use the nearest available earlier observation. If usable CPI data is unavailable, the calculator does not fabricate an inflation value.

Precision and rounding

Core monetary calculations use decimal arithmetic. Money values are rounded to two decimal places using half-up rounding, and share quantities are rounded to six decimal places. Annualized return calculations are reported to two decimal places. Display rounding can therefore create small differences if a reader recomputes a result from already-rounded values shown on screen.

Review and calculation transparency

FomoDejavu uses historical data to illustrate how different investing decisions could have played out. Methodology documentation is reviewed when material data or calculation assumptions change. A named reviewer is shown on a calculator only when that calculator has an explicit page-specific review record.

  • Historical simulations are educational examples, not forecasts or guarantees.
  • Where relevant, results distinguish nominal values from optional inflation-adjusted values.
  • Data coverage varies by instrument and source dataset.
  • Material methodology changes should be reflected by an updated review date on this page.
Editorial Policy Disclaimer

Universal limitations

  • Taxes: Capital-gains tax, dividend withholding, account-specific tax treatment, and other taxes are excluded unless a page explicitly states otherwise.
  • Fees: Brokerage commissions, bid-ask spread, custody costs, and fund expenses are excluded unless explicitly stated.
  • Historical data: Missing, corrected, delisted, or unavailable securities can limit what can be reproduced.
  • Corporate actions: Complex reorganizations may not be fully reconstructed unless represented in the stored data.
  • Currency: Many market comparisons are displayed in USD and may not reflect a reader's local currency exposure.
  • Hypothetical results: Historical performance does not predict or guarantee future results.

Questions? Contact us.