The NoFri Effect: Why Skipping Friday [1]s Beats the Market
A quantitative analysis of day-of-week seasonality in the S&P 500 (2000–2024)
This is one of those topics where the conventional wisdom doesn’t quite hold up.
I’ve spent a lot of time researching this topic, and here’s what I found.
What if one of the simplest alpha generators in equity markets was not a complex algorithm, a neural network, or a macro signal — but a calendar? Specifically: do not trade on Fridays.
Perry Kaufman’s Chapter 4 research on day-of-week seasonality identifies the “NoFri” strategy as a standout performer. His grid search across a multi-stock US equities universe produced a best configuration with a Sharpe ratio of 1.28 and CAGR of 27.23% — numbers that demand scrutiny. This article replicates the core idea on SPY (the S&P 500 ETF), compares three variants, and dissects the behavioral finance behind the pattern.
1. The Kaufman Finding
Kaufman’s grid search optimized five parameters:
Related: index fund investing guide
I think the most underrated aspect here is
Last updated: 2026-04-01
Your Next Steps
- Today: Pick one idea from this article and try it before bed tonight.
- This week: Track your results for 5 days — even a simple notes app works.
- Next 30 days: Review what worked, drop what didn’t, and build your personal system.
About the Author
Written by the Rational Growth editorial team. Our health and psychology content is informed by peer-reviewed research, clinical guidelines, and real-world experience. We follow strict editorial standards and cite primary sources throughout.
Disclaimer: Not investment advice.
Related: All Kaufman Strategies | DCA vs Lump Sum
References
- Kaufman, P. (2019). Trading Systems and Methods, 6th ed. Wiley.
- S&P Global. S&P 500.
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What is the key takeaway about nofri effect?
Evidence-based approaches consistently outperform conventional wisdom. Start with the data, not assumptions, and give any strategy at least 30 days before judging results.
How should beginners approach nofri effect?
Pick one actionable insight from this guide and implement it today. Small, consistent actions compound faster than ambitious plans that never start.
