January barometer
SeasonalityIntermediate
The January barometer, associated with Yale Hirsch, says the direction of January's return in the stock market tends to match the direction of the rest of the year. A mechanical version is long for the following eleven months only if January was up, and in cash or a defensive asset if January was down. It is a once-a-year switch, easy to overfit, and easy to remember only when it works.
Not investment advice. Nothing here is a recommendation to buy or sell anything. Backtests and historical studies are not guarantees, and a rule that worked in one sample can fail in the next. Trading can lose money. Links are for education, not endorsements. Do your own research.
- Rules
- On the last trading day of January, record the sign of the market's January return. If it is positive, hold the risky asset through December. If it is negative, hold cash or the defensive asset named in the rules. Do not override the sign because of a narrative. Revisit the switch only next January.
- Where AI fits
- AI can compute the rule on total-return data for many indexes and many decades without dropping the years that contradict the slogan. It can compare the switch with always being invested, under the same costs. The interesting output is how often the sign is wrong, not a story about one famous year.
- Markets
- Broad equity indexes. Applying it to a single stock is a different, noisier claim.
- Timeframes
- One decision a year. The position is then held for months.
- Risks
- One observation per year is a tiny sample. A few large years drive the folklore. Transaction costs are small, but opportunity cost against a bull market is not. The rule ignores everything that happens after January except its own sign.