TL;DR
Pre-1990 global returns are reconstructed from country-level series in the Dimson-Marsh-Staunton dataset (1900–) and Shiller (US back to 1871). We use GDP-weighted blends with documented assumptions when no direct global series exists.
In short
The honest answer: pre-1990 global data has more uncertainty than US-only Shiller. We document the assumptions in the simulator and offer a 'US only' toggle for users who want the cleaner data series. For most FIRE planners the difference between the two is small.
We're working on a full deep-dive for this article — including historical data, charts, and worked examples. In the meantime, you can run a free simulation to explore the underlying numbers yourself.
Frequently asked questions
- Why is non-US data so much worse before 1990?
- Two world wars, hyperinflations, and capital controls disrupted equity markets in most countries. Reliable index data is hard to assemble. The DMS dataset is the most comprehensive academic source.
- Should I trust pre-1990 global simulations?
- Less than post-1990. For high-stakes planning decisions, lean on the US-only Shiller record where the data is cleanest.
Stress-test your own FIRE plan
FIRE Wealth OS runs your savings rate and expenses against every historical market starting point since 1871. Free to use, no card required.