Reality Check
September 1, 2026

September is the worst month of the year for the S&P 500

It’s also the worst month of the year for 24 other names.

September has a reputation of being a weak month, but the question is not whether the market goes lower in September, but whether a given stock does worse in September than it does the rest of the year. A stock that normally gains 4% a month and gains 2% in September has had a weak September, even though 2% on its own looks fine.

So we backtested 80 large-cap names against their own history. Turns out 69 of the 80 names we checked underperform their own average by a median of 1.74 points.

September is the worst month for SPX

Let’s start with the index. SPX averages −0.59% in September against +0.62% for an average month, which makes September its worst month. The S&P 500 only closes higher 47% of the time in September.

SPX average return by calendar monthEvery month since 1950. Each bar is the average change from the month’s first close to its last close.−0.6%+0.0%+0.6%+1.2%+1.8%Average return+0.96Jan−0.24Feb+0.75Mar+1.44Apr+0.25May+0.04Jun+1.00Jul+0.05Aug−0.59Sep+0.83Oct+1.52Nov+1.45Dec

Individual names diverge sharply

The difference between individual names is much larger. AEHR averages +7.43% in September versus +3.38% in a typical month. AMZN and NKE also have better than average months in September, and it’s NKE’s strongest month of the year.

On the other hand, CELH averages −7.84% in September against +3.35% in a typical month and has closed lower in each of its last four Septembers.

Widest September gaps in either directionCovers 80 names with at least 10 Septembers of history.A bar to the right means September outperforms a typical month for that stock.−12 pts+0 pts+12 ptsAEHR+4.04AMZN+2.36NKE+2.11ORCL+1.46ABBV+1.03GOOGL+0.97AMAT−4.64LITE−4.75ASML−5.38AMD−5.68AAPL−5.77CELH−11.18September average minus the same stock’s average monthSeptember is strongerSeptember is weaker

AEHR and AMZN rank among the 6 strongest September performers, while CELH, AAPL and AMD sit among the 6 weakest.

All 80 names we checked, sorted by gap size

All 80 names we checked, sorted by September gap
Gap is each stock’s September average minus its own average month, in percentage points.
TickerSeptember AvgAvg MonthGapSeptember RankSeptember HigherSeptembers
AEHR+7.43%+3.38%+4.042 of 1248%29
AMZN+5.74%+3.38%+2.363 of 1259%29
NKE+3.40%+1.28%+2.111 of 1262%45
ORCL+3.37%+1.91%+1.463 of 1257%40
ABBV+2.28%+1.25%+1.035 of 1254%13
GOOGL+3.02%+2.04%+0.975 of 1264%22
DELL+4.13%+3.18%+0.953 of 1290%10
CPER+1.48%+0.66%+0.822 of 1250%14
STX+2.50%+1.96%+0.546 of 1252%23
LULU+2.21%+1.72%+0.496 of 1263%19
QCOM+2.54%+2.34%+0.205 of 1262%34
BABA+0.63%+0.64%−0.016 of 1233%12
LMT+0.71%+0.77%−0.065 of 1259%64
CVX+0.40%+0.63%−0.226 of 1259%64
LHX+0.71%+0.95%−0.248 of 1257%44
CRM+1.60%+1.87%−0.268 of 1250%22
IBKR+0.52%+0.81%−0.298 of 1263%19
TSLA+3.67%+4.18%−0.507 of 1263%16
GE+0.22%+0.83%−0.618 of 1247%64
MCD+0.49%+1.12%−0.638 of 1255%60
SBUX+1.17%+1.88%−0.708 of 1256%34
META+1.11%+1.85%−0.747 of 1250%14
MSFT+1.22%+1.96%−0.7410 of 1268%40
GLD+0.05%+0.81%−0.7610 of 1243%21
DPZ+0.98%+1.76%−0.788 of 1264%22
PG−0.16%+0.67%−0.8210 of 1248%64
IBM−0.26%+0.58%−0.8410 of 1253%64
AVGO+2.26%+3.23%−0.977 of 1259%17
JNJ+0.03%+1.03%−0.9910 of 1250%64
COST+0.00%+1.20%−1.209 of 1243%40
SPX−0.59%+0.62%−1.2112 of 1247%76
UNH+0.65%+1.89%−1.249 of 1246%41
MA+0.62%+2.05%−1.4311 of 1255%20
AAL+0.07%+1.53%−1.468 of 1257%21
UEC+0.83%+2.31%−1.476 of 1253%19
SMCI+1.04%+2.57%−1.537 of 1253%19
LLY−0.56%+1.00%−1.5612 of 1248%54
ADBE+0.41%+2.03%−1.629 of 1260%40
MSTR+1.52%+3.14%−1.626 of 1254%28
XLF−1.27%+0.44%−1.7111 of 1241%27
PEP−1.01%+0.75%−1.7612 of 1244%54
BA−0.90%+0.93%−1.8211 of 1252%64
GS−0.78%+1.08%−1.8611 of 1252%27
IGV−0.97%+0.89%−1.8711 of 1252%25
WMT−0.45%+1.43%−1.8711 of 1246%54
F−1.43%+0.52%−1.9511 of 1246%54
TXN−0.85%+1.16%−2.0111 of 1254%54
NOW+0.44%+2.48%−2.0410 of 1250%14
IWM−1.50%+0.62%−2.1212 of 1246%26
CAT−1.16%+1.02%−2.1812 of 1242%64
FSLR−0.03%+2.17%−2.2010 of 1253%19
INTC−0.94%+1.41%−2.3512 of 1246%46
MU−0.10%+2.29%−2.3811 of 1248%42
KO−1.69%+0.72%−2.4112 of 1239%64
QQQ−1.65%+0.82%−2.4712 of 1252%27
PANW+0.19%+2.92%−2.7310 of 1243%14
HD−0.81%+1.93%−2.7312 of 1249%45
TSM−1.38%+1.39%−2.7712 of 1254%28
HAL−1.96%+0.85%−2.8012 of 1248%54
SOXX−1.71%+1.15%−2.8612 of 1248%25
DIS−1.77%+1.12%−2.8912 of 1244%64
SLV−2.15%+0.78%−2.9311 of 1245%20
JPM−2.01%+0.96%−2.9612 of 1246%46
HON−2.39%+0.59%−2.9812 of 1242%64
PYPL−2.38%+0.65%−3.0311 of 1227%11
FTNT−0.48%+2.76%−3.2312 of 1250%16
SMH−2.46%+0.94%−3.4012 of 1246%26
V−1.95%+1.48%−3.4312 of 1239%18
BAC−2.59%+0.85%−3.4412 of 1243%53
NFLX−0.25%+3.23%−3.4811 of 1258%24
MS−2.81%+1.20%−4.0212 of 1248%33
NVDA−0.25%+3.79%−4.0510 of 1256%27
SHOP+0.19%+4.31%−4.129 of 1255%11
MRVL−2.28%+1.98%−4.2512 of 1246%26
AMAT−2.65%+1.99%−4.6412 of 1237%46
LITE−1.40%+3.35%−4.7511 of 1227%11
ASML−3.13%+2.25%−5.3812 of 1239%31
AMD−3.57%+2.11%−5.6811 of 1237%46
AAPL−3.90%+1.87%−5.7712 of 1240%45
CELH−7.84%+3.35%−11.1812 of 1226%19

September is the worst month of the year for 25 of the 80: SPX, LLY, PEP, IWM, CAT, INTC, KO, QQQ, HD, TSM, HAL, SOXX, DIS, JPM, HON, FTNT, SMH, V, BAC, MS, MRVL, AMAT, ASML, AAPL and CELH. For 48 of them it lands in the bottom 3.

Measured against its own average month, September is weaker for 69 of the 80 names we tested, by a median of 1.74 points. The S&P 500 itself averages just −0.59% in September versus +0.62% in a typical month.

The gap between individual stocks is large. AEHR runs 4.04 points above its own average in September. CELH runs 11.18 points below.

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