Should you invest in September?

Seasonal backtest · JPI Fair (balanced) method on the S&P 500 · 2015-2024

In short — historically (2015-2024, JPI Fair method on the S&P 500), buying in early September and holding 12 months returned +15.5%/yr on average — the 10th best of the 12 months. $1000 would have become $3937 in 10 years (the S&P 500 index did +13.2%/yr on the same basis). Best month: November; worst: August. ⚠️ Only 10 years: a tendency, not a guarantee.

Below is the 12-month entry ranking (JPI Fair method, S&P 500, 2015-2024) — September is highlighted — then the year-by-year detail for buying in early September.

#	Month	Return / yr	Ratio	$1,000 becomes (10y)	S&P 500 comparison
1	November	+25%	1.32	$8,272	+13.7%
2	January	+24.4%	0.83	$6,705	+12.2%
3	December	+23.1%	1.14	$7,013	+13.2%
4	February	+20%	0.97	$5,275	+12.4%
5	October	+18.7%	1.22	$5,042	+14.1%
6	March	+17.3%	0.82	$4,168	+11.7%
7	May	+16.9%	0.83	$4,144	+11%
8	June	+16.1%	0.81	$3,855	+11.4%
9	April	+15.7%	0.53	$3,241	+11.7%
10	September	+15.5%	1.14	$3,937	+13.2%
11	July	+14.9%	0.71	$3,372	+12.3%
12	August	+14.1%	1.11	$3,530	+12.1%

📖 How to read this table — method used: JPI Fair (the balanced formula — buy stocks where at least 2 analysts reliable on their sector are bullish, taking the median of their targets). Our recommended formula.

• Return / yr: average annual gain of that selection if you buy that month, over 2015-2024.
• Ratio: return ÷ volatility — higher means steadier results (S&P 500 ≈ 0.9).
• $1000 becomes (10y): what $1000 invested that month each year would become after 10 years (compounded).
• S&P 500 comparison: the average S&P 500 return over the same period — far more stable regardless of the month.

Year by year — buy early September

Year	Return (buy early September)
2025 ⏳	+28.8% (in progress)
2024	+20.2%
2023	+24.6%
2022	+24.3%
2021	-10.2%
2020	+42.2%
2019	+6.5%
2018	+4.8%
2017	+17.7%
2016	+18.5%
2015	+6.4%

💡 Keep in mind: this comes from just 10 cycles. The robust research message is that staying invested beats waiting for a specific month. Use this ranking as an insightful curiosity, not a buy signal.

📊 Interactive version — September, 3 universes, filters →

↔️ Other months — ← August · 12-month ranking · October →

FAQ

Is September a good time to invest?

Over 2015-2024, buying in early September (JPI Fair method, S&P 500) returned +15.5%/yr on average, the 10th best of the 12 months. But 10 years is little: it's a tendency, not a guarantee, and the entry month matters less than staying invested.

What would $1000 invested in September have become?

On average over 2015-2024, $1000 invested in early September each year (12-month hold, JPI Fair method) would have become about $3937, versus the S&P 500 index on the same basis.

What is the best month to invest compared to September?

In our 2015-2024 ranking, November comes first. September is the 10th best. See the full 12-month ranking above.

What is JPI Invest?

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🏆 Analyst leaderboard by real reliability (beating their sector, not just riding the rally)
🎯 What to buy: 3 backtested methods over 11 years, from cautious to aggressive
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⚠️ Educational analysis, not investment advice. Point-in-time backtest on recomputed Yahoo data, short sample. Past performance does not predict the future.