Wealth Inequality (Yard-Sale Model)
The yard-sale model is the simplest economy that produces extreme inequality from perfectly fair rules. Every agent starts with the same wealth; each tick random pairs trade, staking a fraction of the poorer partner’s wealth on a fair coin flip. No agent is smarter, luckier or better connected — yet wealth inexorably concentrates until one agent holds nearly everything. This simulator animates the wealth histogram, draws the Lorenz curve with a live Gini coefficient, and reports the top-10% and top-1% shares as concentration builds. A bias slider tilts the coin toward the richer or poorer trader, and a redistribution slider levies a small flat wealth tax every few ticks — enough, it turns out, to hold the whole distribution in a stable steady state.
Runs 100% in your browser — simulations are computed locally on your device.
Read the full guide to this tool
Notes
- Fairness of each trade is not enough: staking a share of the poorer agent’s wealth makes losses hurt the poor proportionally more, and repeated fair bets drive wealth toward total concentration (Boghosian’s “oligarchy” result).
- The Gini coefficient is twice the area between the Lorenz curve and the diagonal of perfect equality: 0 means everyone equal, 1 means one agent owns it all — watch it climb toward 1 with no redistribution.
- Multiplicative luck compounds: a lucky streak grows your stake for the next flip, an unlucky one shrinks it — the same mathematics that makes lognormal-ish wealth distributions with heavy tops.
- A small flat redistribution — a fraction of a percent of wealth per round — is enough to balance the concentrating force and produce a stationary, unequal but stable distribution, the model’s version of a wealth tax.
- Runs 100% in your browser — simulations are computed locally on your device.
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