Average return and win-rate by weekday for one instrument

Code snippets

curl "https://api.oanor.com/calendareffects-api/v1/dayofweek" \
  -H "x-oanor-key: oanor_test_..."

await fetch("https://api.oanor.com/calendareffects-api/v1/dayofweek", {
  headers: { "x-oanor-key": "oanor_test_..." }
});

$ch = curl_init("https://api.oanor.com/calendareffects-api/v1/dayofweek");
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-oanor-key: oanor_test_..."]);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$out = curl_exec($ch);

import requests
requests.get(
    "https://api.oanor.com/calendareffects-api/v1/dayofweek",
    headers={"x-oanor-key": "oanor_test_..."}
)

Example response

A real response from this endpoint, captured by the latest health check.

{
    "data": {
        "days": {
            "Friday": {
                "count": 254,
                "win_rate_pct": 52.8,
                "avg_return_pct": 0.0115
            },
            "Monday": {
                "count": 234,
                "win_rate_pct": 62.4,
                "avg_return_pct": 0.112
            },
            "Tuesday": {
                "count": 261,
                "win_rate_pct": 49.8,
                "avg_return_pct": 0.0248
            },
            "Thursday": {
                "count": 252,
                "win_rate_pct": 51.6,
                "avg_return_pct": -0.01
            },
            "Wednesday": {
                "count": 259,
                "win_rate_pct": 56,
                "avg_return_pct": 0.1158
            }
        },
        "name": "S&P 500 ETF",
        "note": "Average daily return and win-rate by weekday over window_days. Equity ETFs trade Mon-Fri; crypto trades all seven days. Descriptive of historical tendency, not predictive. Read fresh per call, nothing cached.",
        "class": "index",
        "source": "Yahoo Finance",
        "symbol": "SPY",
        "best_day": "Wednesday",
        "worst_day": "Thursday",
        "window_days": 1260
    },
    "meta": {
        "timestamp": "2026-06-12T10:34:39.725Z",
        "request_id": "74a710f8-26ee-4b6b-b7d6-f2ea1458533b"
    },
    "status": "ok",
    "message": "Day-of-week retrieved successfully",
    "success": true
}