When Was the Last Blue Moon
The last blue moon was the seasonal blue moon on August 19, 2023, which is the third full moon in a four full moon season, according to timeanddate.com. The next blue moon is the calendrical blue moon on May 31, 2026, which is the second full moon in a single calendar month.
A blue moon is a calendrical or seasonal term for an extra full moon, not a literal blue colored moon, as explained by NASA's Earth Observatory. In finance, the term is used as a reference point for rare event timing, calendar anomalies, and seasonal liquidity patterns.
Blue Moon Frequency and Calendar Impact
A calendrical blue moon occurs roughly every 2.5 to 3 years, while a seasonal blue moon occurs about every 2.5 years, based on the Maine Farmers' Almanac rule used by timeanddate.com. The next calendrical blue moon on May 31, 2026, follows the August 19, 2023, seasonal blue moon, creating a gap of more than two years between events.
In market calendars, the blue moon cycle is tracked by quantitative analysts as a low frequency time marker for backtesting seasonal strategies, as noted in research summaries on Forbes. The rarity of the event makes it a focus for calendar effect studies, alongside other lunar and seasonal anomalies.
Blue Moon and Financial Market Behavior
Some quantitative studies examine whether the blue moon period affects volatility, trading volume, or sentiment, with mixed results and no statistically robust causal link to returns, as discussed in market analysis on Forbes. The effect, if any, is small compared to macroeconomic drivers such as interest rates, inflation, and earnings cycles.
Institutional investors and asset managers use the blue moon as a calendar curiosity rather than a trading signal, focusing instead on fundamentals and policy data from sources like the U.S. Securities and Exchange Commission. The next blue moon on May 31, 2026, will be monitored as a date marker, but strategy decisions remain tied to economic indicators and company performance.