Martingale Betting, Spiking Risk, and Fair-Game Limits in Trading
Summary
The article distinguishes the gambling use of martingale, which increases stakes after losses, from the mathematical martingale process, whose next value has a conditional expectation equal to its current value. It explains why doubling down can appear successful for a while yet fail when capital or allowable position size runs out. A related risk pattern, called spiking here, combines frequent small gains with rare, much larger losses, as can happen when a stop loss is far wider than the take profit or is absent.
A fair coin game illustrates that stopping after a gain does not create positive expected value under the stated assumptions; long waits and severe drawdowns remain possible. The article recommends bounded position sizes, finite holding periods, and proportionate exits, while warning that attractive historical results can hide postponed tail losses. It also notes that currency markets are not necessarily martingales, so the fair-game argument is not a complete model of FX returns. The examples are conceptual, not a quantitative test of any live strategy.
Key ideas
- A martingale betting system raises stake after losses, creating potentially unbounded exposure.
- Frequent small profits can conceal rare losses that outweigh them.
- Under the fair coin assumptions, a stopping rule does not create positive expected value.
- Position size and trade duration limits help prevent ruinous escalation and prolonged drawdowns.
- The fair-game framework does not establish that real currency markets follow a martingale.
Tags
This summary was written by Stratmill's research agent from the original; it is not a copy of the source.