Wall Street's "sell in May and go away" mantra is back in focus as markets approach what's widely seen as the weakest stretch of the year, but fresh data suggests the seasonal playbook may be badly outdated.

Bank of America's chief technical strategist Paul Ciana challenged the decades-old rule this week, saying historical trends show equities often hold up through early summer rather than rolling over immediately.

BofA Just Killed The Sell In May Trade: Here’s What Replaces It

First, Ciana ran the numbers on every six-month rolling window for the S&P 500 since 1928.

May through October is indeed the weakest stretch on the calendar, up 66% of the time with a 2.47% average return. November through April is the strongest, up 70% of the time with a 5.20% average.

So far, so familiar.

But the weakness is not where the saying suggests.

S&P 500 Seasonality (6-Month Periods)

6-month period

Avg Return

Median Return

% Time Up

Avg Drawdown

Median Drawdown

Jan, Jun

3.85%

5.01%

65.3%

-7.60%

-5.92%

Feb, Jul

3.98%

4.56%

68.4%

-7.90%

-4.85%

Mar, Aug

4.98%

4.94%

70.4%

-7.58%

-5.39%

Apr, Sep

3.54%

3.94%

66.3%

-7.79%

-4.29%

May ...