OriginaveIs there a best month to buy ETFs?
Average S&P 500 returns for every calendar month, the best day of the month to invest, and whether “sell in May” survives contact with the data — from real CSP1 prices, measured in pounds from the LSE line, currency swings included.
Across 2010–2026, July has been the strongest calendar month for the S&P 500 as tracked by CSP1: +2.76% on average, positive in 76% of years. September has been the weakest at -1.93%. That gap — 4.7 percentage points between the extremes — is the entire seasonal effect, and it comes with no promise of repeating next year.
Average return by calendar month
| Month | Average return | Positive years | Best | Worst |
|---|---|---|---|---|
| January | +0.70% | 50% | +9.92% (2013) | -6.02% (2022) |
| February | +1.40% | 75% | +6.18% (2013) | -6.88% (2020) |
| March | +0.48% | 69% | +7.08% (2022) | -7.76% (2025) |
| April | +0.54% | 38% | +9.26% (2020) | -3.84% (2025) |
| May | +2.06% | 69% | +6.98% (2013) | -2.62% (2022) |
| June | +1.33% | 76% | +8.88% (2016) | -5.27% (2010) |
| July | +2.76% | 76% | +8.35% (2022) | -2.86% (2011) |
| August | +0.12% | 59% | +6.16% (2020) | -9.08% (2011) |
| September | -1.93% | 50% | +3.72% (2011) | -31.58% (2010) |
| October | +2.22% | 69% | +6.84% (2015) | -4.77% (2018) |
| November | +2.32% | 81% | +6.90% (2020) | -1.57% (2022) |
| December | +0.91% | 69% | +9.34% (2010) | -8.34% (2018) |
195 complete calendar months of CSP1, measured in pounds from the LSE line, currency swings included, 2010–2026.
Is there a best day of the month to buy ETFs?
Sort of — but not for the reason timing fans hope. Because markets drift upward over time, the earlier in the month you buy, the cheaper you get in on average. No mid-month sweet spot, no month-end discount: just drift. The honest conclusion is that the best day of the month to buy an ETF is the earliest one your payday allows.
| Always buying on… | vs the month’s average price | Cheaper than average |
|---|---|---|
| First trading day | -0.44% | 64% of months |
| The 5th (or next trading day) | -0.26% | 62% of months |
| The 10th (or next trading day) | +0.05% | 52% of months |
| The 15th (or next trading day) | +0.01% | 44% of months |
| The 20th (or next trading day) | -0.01% | 42% of months |
| The 25th (or next trading day) | +0.18% | 42% of months |
| Last trading day | +0.35% | 37% of months |
Each row: buy CSP1 on that day every month of 2010–2026 and compare the price paid with that month’s average price.
Does “sell in May and go away” hold up?
The famous half-year gap shows up in CSP1’s data — but notice what the slogan skips: the “bad” summer half still averaged +8.82%. Selling in May meant giving that up, then paying the trading costs and taxes for the privilege.
Do other funds agree?
A seasonal pattern that only exists in one fund is noise. The cross-check: best and worst calendar months for the other big funds we track — same method, each over its own history.
The honest take
Seasonal averages describe the past; they don’t schedule the future. The average month of CSP1 returned +1.08% across 2010–2026 — so every month spent waiting for a “better” one had that expected cost, while the seasonal spread is a fraction of a single bad (or great) week. If a calendar rule helps you invest regularly, keep it. Just don’t expect it to beat simply starting today.
Frequently asked
What is the best month to buy the S&P 500?
July, in this data: across 2010–2026 it averaged +2.76% for CSP1 and finished positive in 76% of years. The seasonal edge is small and unreliable, though — being invested at all matters far more than which month you start.
What is the worst month for stocks?
September has the weakest average in this window: -1.93% per year for CSP1, positive in only 50% of years. September's classic bad reputation is confirmed here.
Is there a best day of the month to buy ETFs?
Earlier beats later, but only because markets drift upward. Always buying CSP1 on the first trading day cost -0.44% vs the month's average price across 2010–2026; always waiting for the last trading day cost +0.35%. The best day of the month to buy an ETF is simply the earliest one your payday allows.
Does “sell in May and go away” actually work?
The gap is real in this data — November–April averaged +6.67% while May–October averaged +8.82%, and winter won 8 of 15 cycles. But the summer half still averaged a gain, so selling in May meant skipping +8.82% on average, plus trading costs and taxes.
Does S&P 500 seasonality look different in pounds?
All figures on this page are measured in pounds from the LSE line, currency swings included — so the answer already reflects what a pounds-based buyer of CSP1 experienced, exchange rate and all. Currency moves can flip a month's sign versus the USD version of the same index.
Dig deeper
Follow one year month by month on the monthly returns dashboard, test a starting point with the what-if calculator, or see whether investing everything at once beats spreading it out under lump sum vs DCA. The numbers behind this page live on the CSP1 fund page, and the currency side of these figures is explained in the currency effect.