# Day-of-week Effects

Also known as: Monday effect, turnaround Tuesday.
A Time, Sessions & Seasonality concept (Calendar effects) in the LuxAlgo Library, with 5 indicator implementations.

## What are Day-of-week Effects?

Day-of-week effects are calendar tendencies in which average return, volatility, or volume differs by weekday. The classic examples come from the equity literature: the Monday (or weekend) effect, where Mondays showed the weakest average returns in twentieth-century US stock data, and 'turnaround Tuesday', the folk tendency for Tuesday to reverse Monday weakness. Measurement is simple: bucket daily returns by weekday and compare each bucket's average return, win rate, and range, the same machinery as [month-of-year seasonality](https://www.luxalgo.com/library/concept/month-of-year-seasonality/) at a finer grain.

The anomaly has real academic pedigree. Frank Cross documented the Friday-strong, Monday-weak pattern in Standard & Poor's index data in 1973, Kenneth French's 1980 weekend-effect study made it one of the most cited calendar anomalies in finance, and Gibbons and Hess soon extended the evidence beyond equities. Proposed explanations included weekend news timing, the settlement conventions of the era, and investor mood; none was ever settled, and none gave a reason to expect permanence.

Two caveats define the concept. The measured effects are small relative to daily noise, so they only appear in aggregates, and several classic anomalies weakened or vanished in the decades after publication. Weekday statistics are context to re-verify on your own market and sample, often alongside [intraday time-of-day effects](https://www.luxalgo.com/library/concept/intraday-time-of-day-effects/), not standing edges.

Doing the measurement well matters more than the folklore. Five weekday buckets across many instruments and lookbacks invite data mining, so a tendency worth attention should survive subsample splits, have a plausible driver, and be large enough to clear costs. Structural drivers age best: weekly options expiry, futures roll flows, and the concentration of releases on [macro event days](https://www.luxalgo.com/library/concept/macro-event-days/) (US employment reports on Fridays, Fed decisions on Wednesdays) give some weekdays a mechanical character that return averages miss.

For most traders the practical payoff is structure rather than direction. In markets with defined [trading sessions](https://www.luxalgo.com/library/concept/trading-sessions/), Monday opens on a weekend of accumulated news and can gap, while Friday afternoons carry expiry mechanics and pre-weekend position squaring. In 24/7 venues such as crypto the week still shows up through thinner weekend participation. Weekday tendencies sit between intraday effects and monthly or [longer calendar cycles](https://www.luxalgo.com/library/concept/long-horizon-calendar-cycles/), and read best alongside both.

## How to Measure Day-of-week Effects

A weekday profile takes minutes with a seasonality tool or a spreadsheet export:

1. Take several years of daily bars at minimum, planning to split the sample into at least two subperiods.
2. Bucket each close-to-close return by weekday, or apply a day-of-week distribution indicator that does the grouping on the chart.
3. Compare each weekday's average return, median return, and win rate, then repeat for range and volume, usually the steadier statistics.
4. Re-run the buckets per subperiod; a tilt that exists in one half of the data and not the other is noise until proven otherwise.
5. Tag scheduled events before crediting the weekday itself: recurring weekday behavior often turns out to be the economic calendar in disguise.
6. For session-based markets, repeat the exercise on [regular-hours data](https://www.luxalgo.com/library/concept/rth-vs-eth/); including overnight moves can flip which weekday looks strong.

## How traders use it

- Profiling a market's week: bucketing range and volume by weekday shows where movement historically concentrates, which helps schedule attention and avoid forcing trades into typically quiet sessions.
- Filtering a strategy: testing whether a system's results concentrate on particular weekdays before adding a day filter, with out-of-sample checks so noise is not mistaken for pattern.
- Planning around recurring flows: weekly closes, options expiries, and Monday gaps give some weekdays a distinct character worth preparing for even when average returns are statistically indistinguishable.
- Managing weekend risk: where markets gap across the close, Friday reviews of size and stops apply weekday thinking to risk rather than prediction, informed by [session open/close behaviors](https://www.luxalgo.com/library/concept/session-open-close-behaviors/).
- Keeping the statistic current: [seasonality tooling](https://www.luxalgo.com/library/concept/seasonality-tooling/) that renders weekday distributions on the chart replaces remembered folklore with the live number for the instrument at hand.

## Day-of-week Effects vs Related Calendar Concepts

- **Month-of-year Seasonality** (https://www.luxalgo.com/library/concept/month-of-year-seasonality/): The same bucketing logic at coarser grain: twelve monthly buckets instead of five weekday ones. A weekday recurs about fifty times a year while a month recurs once, so weekday statistics stabilize sooner. Both are small tendencies demanding out-of-sample checks.
- **Intraday Time-of-day Effects** (https://www.luxalgo.com/library/concept/intraday-time-of-day-effects/): The next level down: behavior that varies by hour or session segment within the day. The two interact, since a Friday afternoon does not trade like a Tuesday afternoon, and serious calendar work conditions on both at once.
- **Macro Event Days** (https://www.luxalgo.com/library/concept/macro-event-days/): Event-anchored rather than calendar-anchored. Payrolls Fridays and Fed Wednesdays leak scheduled volatility into weekday buckets, so separating event days from ordinary ones sharpens both statistics.
- **Fixed Time Cycles** (https://www.luxalgo.com/library/concept/fixed-time-cycles/): Fixed-length periodicities hunted in price itself. Day-of-week analysis starts from a known five-day calendar period; cycle tools search for whatever period the data suggests, calendar or not.

## FAQ

### Is the Monday effect still real?

It was well documented in older US equity data, where Monday average returns were the weakest of the week, but studies covering recent decades find the effect faded or even reversed after it became widely known. Treat it as a historical anomaly to re-verify on current data for your specific market, not as a dependable standing edge.

### What is turnaround Tuesday?

It is trader shorthand for the tendency of markets to bounce on Tuesday after a weak Monday, especially during pullbacks. It shows up as a loose base rate in some samples and not in others, so check the statistic on your instrument and period before leaning on it; it is folklore first, measured effect second.

### What causes day-of-week effects?

No single cause is settled. Candidates include news timing around the weekend, older settlement conventions, options expiry and hedging flows, and behavioral stories about mood. The most durable drivers are structural and scheduled, which is why many weekday patterns are better understood as event patterns in calendar disguise.

### Do day-of-week effects exist in crypto?

Crypto trades continuously, so the week expresses itself through participation rather than exchange hours: weekends typically trade thinner, which changes how moves develop. Published findings on weekend return tendencies in bitcoin conflict across samples, which is the real lesson: test current data before trusting any claimed weekday edge.

### Are day-of-week effects strong enough to trade on their own?

Rarely. Return differences by weekday are small relative to daily volatility and to costs, and they drift over time. They earn their keep as filters, scheduling aids, and context; a standalone weekday system should be treated as a data-mining red flag.

### What is the weekend effect?

The older name for the Monday effect: returns measured from Friday's close to Monday's close were historically the weakest of the week in US equities, implicating the weekend itself. Later studies found the pattern faded after publication, and some recent samples show it inverted.

## Implementations in the Library

- Day Of Week Price Distribution (LuxAlgo): https://www.luxalgo.com/library/indicator/day-of-week-price-distribution/
- Seasonality Widget (LuxAlgo): https://www.luxalgo.com/library/indicator/seasonality-widget/
- Buy Sell Calendar (LuxAlgo): https://www.luxalgo.com/library/indicator/buy-sell-calendar/
- Periodic Activity Tracker (LuxAlgo): https://www.luxalgo.com/library/indicator/periodic-activity-tracker/
- Weekly Stacked Daily Changes (LuxAlgo): https://www.luxalgo.com/library/indicator/weekly-stacked-daily-changes/

## Related concepts

- Month-of-year Seasonality: https://www.luxalgo.com/library/concept/month-of-year-seasonality/
- Turn-of-month Effects: https://www.luxalgo.com/library/concept/turn-of-month-effects/
- January Effect: https://www.luxalgo.com/library/concept/january-effect/
- Buyback Blackout Windows: https://www.luxalgo.com/library/concept/buyback-blackout-windows/
- Macro Event Days: https://www.luxalgo.com/library/concept/macro-event-days/
- Pre-holiday Drift: https://www.luxalgo.com/library/concept/pre-holiday-drift/
- Santa Claus Rally: https://www.luxalgo.com/library/concept/santa-claus-rally/
- sell-in-May: https://www.luxalgo.com/library/concept/sell-in-may/
- Quarterly Earnings Season Phases: https://www.luxalgo.com/library/concept/quarterly-earnings-season-phases/
- Tax-loss Selling Season: https://www.luxalgo.com/library/concept/tax-loss-selling-season/

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Source: https://www.luxalgo.com/library/concept/day-of-week-effects/ (LuxAlgo Library, the encyclopedia of trading & technical analysis). Free to use with attribution: https://www.luxalgo.com/library/license/