The Santa Claus Rally Meets Data
Still a Tailwind, But Not the Signal Everyone Thinks
The first half of December has been strong again this year.
Twitter/X is full of “strap in, Santa is coming early!” takes.So I wondered… does a strong early December statistically lead to a stronger finish?
This analysis uses 40+ years of SPX, NDX, and RTY returns with institutional-quality statistical testing.
What Always Matters: 2H December Seasonality
Historically, 2H December is where the party is. SPX: +1.1%, NDX: +1.5%, RTY: +2.5%.
Hit rates: 65–81%. Good odds. Good returns.
In rate-cut years? Even better. The Fed is a powerful Santa.
Plain and simple assumption from the Data I modeled:
Base case = supportive backdrop into year-end.
The Myth
The common belief amongst Retail Traders and on X right now:
“Strong 1H December → Guaranteed Santa Rally”Data says: No.
SPX: Neutral → Slight bump (+0.28%)
RTY: Neutral → Basically unchanged (-0.26%)
NDX: Reversal risk (-1.41%)
From my findings it seems:
Seasonality is a tailwind — not a trigger.
Index Deep Dive
SPX: Still bullish, but edge doesn’t improve SPY 0.00%↑
From this graph we see that strong starts don’t worsen OR strengthen the outcome for SPX.
SPX / SPY 0.00%↑ 2025 sits right in the historically normal cluster. Which I view as a great sign when interpreting historical seasonality to guide future results.
NDX: Doesn’t like early December strength QQQ 0.00%↑
It appears that Tech tends to mean-revert after a strong start.
The only index where 1H strength is negative information.
The best years (ex: 2009) actually started soft.
A warning I’d note…
NDX / QQQ 0.00%↑ is the most vulnerable if the Santa narrative gets crowded.
RTY: Your friend in 2H December IWM 0.00%↑
Small caps remain the seasonal powerhouse of December.
Hit rates lead every group.
Caption:
RTY / IWM 0.00%↑ is where the actual statistical edge lives.
What Actually Matters for the Next 3 Weeks
Even if 1H-December isn’t a signal, the bigger forces still favor a constructive tape into year-end. I am constructively Bullish for Year-End.
Positioning
Under-exposed institutions are being dragged back in — FOMO is real as the tape grinds higher. (FOMO = Fear of Missing Out)
Retail remains active, liquidity is healthy, and flows continue to influence price action.
Buybacks are re-accelerating into their strongest seasonal window of the year.
Systematic strategies are re-levering as volatility resets lower → mechanical bid underneath the market.
January Effect ahead: massive household portfolio rebalance historically pulls flows into equities.
The flow of capital still leans supportive. The why matters more than the calendar myth. Source: Citadel Securities
Bottom Line — Clean Takeaway
🎅 Strong 1H December doesn’t drive returns — buttttt…
SPX → Constructive, but not because of 1H performance SPY 0.00%↑
NDX → Be selective, watch positioning / crowding risk QQQ 0.00%↑
RTY → Best seasonal tailwind (especially if soft-landing narrative continues) IWM 0.00%↑
Here’s what I’m seeing from all of this data I’ve analyzed for you:
Santa shows up — but he’s not coming early just because we had a good 1H (so far).
Pay attention to 2H Dec because it appears it’s going to be a great one!
Thanks for reading! Before I let you go, here’s a quick note:
Merry Christmas, everyone!
I hope you’re able to enjoy this special time of year with the people who matter most.
Thank you for your continued support — it’s what makes this possible, and I’m truly grateful for each and everyone of you!
Wishing you all a Merry Christmas and God Bless! ✨🎄