What the September Effect Can Teach Marketers About Long-Term Growth

If you follow the stock market, you know September has a reputation for being a bad month.

What is the "September Effect"?

The so-called September Effect refers to the historical tendency for stocks to perform worse in September than other months. Since 1950, the S&P 500 has averaged a -0.68% return in September and finished the month positive only 44% of the time. It’s not a prediction; it’s a historical pattern, but it isn’t bad every year.

No, this blog isn’t about the stock market, but we think marketers can learn something from the September Effect.

Marketing performance can be similar. One slow month doesn't necessarily mean your strategy is broken. One successful campaign doesn't mean you've cracked the code. And one disappointing quarter shouldn't automatically send your team searching for a new strategy.

Instead, marketers should look beyond the short-term noise and focus on what drives sustainable growth.

But First, Why Does Long-Term Marketing Matter?

B2B buyers form opinions way before they engage sales.

6sense found that 95% of B2B buyers ultimately purchase from a vendor that was already on their Day One shortlist. Even more telling, 94% of buyers said they had already ranked their shortlist before contacting a seller.

That means the work marketers do before a buyer is actively talking to sales can have a major impact on future revenue.

The B2B buying cycle is lengthy- the average buying cycle was 10.1 months in 2025, according to 6sense.

The takeaway: Marketing shouldn't be judged entirely by what happens this month. Some of your most important work is influencing the buyers who aren't ready to buy yet.

What Can Marketers Learn From The September Effect?

1. Don't Overreact to One Bad Month

If you have a month when traffic is down, leads are coming in more slowly, and conversion rates dip, don’t panic!

Short-term fluctuations are normal. Seasonality, market conditions, changes in buyer behavior, campaign timing, and countless other factors can affect performance.

Before changing your entire strategy, look for a pattern.

Ask: Is this a one-month problem or a trend?

Compare performance over multiple months or quarters before making major decisions.

Remember, 95% of B2B buyers purchase from a vendor that was already on their Day One shortlist. Your marketing performance isn't always reflected in the leads coming in today. 

2. Balance Short-Term and Long-Term Goals

It's easy to prioritize activities that produce immediate results. Paid campaigns generate leads. Email campaigns generate clicks. Sales promotions generate opportunities. But not every marketing investment is designed to produce a lead tomorrow.

Brand awareness, thought leadership, SEO, content, and audience building can take longer to influence the pipeline.

LinkedIn's B2B Institute highlights the 95-5 Rule: roughly 95% of B2B buyers are out of market at any given time, meaning most potential buyers aren't ready to make a purchase today.

3. Look for Patterns, Not Predictions

The September Effect exists because there's a historical pattern, but that doesn't mean investors can predict exactly what will happen every September. Marketing is similar.

Your data can tell you what has happened. It can help you identify trends and make better decisions. But it doesn't guarantee what will happen next.

In 2025, B2B buyers evaluated an average of 5.1 vendors, up from 4.5 the previous year. (6sense)

This means there are plenty of variables influencing the outcome of a purchase.

Instead of asking:

"Why did leads drop this month?"

Ask:

"What is this data telling us about our performance over time?"

Look at trends across channels, campaigns, audiences, and quarters before deciding what needs to change.

4. Don't Abandon What Is Working

When performance slows down, it’s easy to fall into the "new tactic" trap. This could mean a new campaign or a new tool. 

You rarely need these things; it’s better to take advantage of what you already have, like:

• Refreshing underperforming content
• Improving conversion paths
• Testing new messaging
• Revisiting your audience
• Strengthening campaigns that have historically worked

There's another reason to stick with it: 44% of B2B buyers say it's rare to come across relevant B2B marketing, according to Adobe. This means there’s often more opportunity in making your existing marketing more relevant than just creating something new.

5. Build for the Future

B2B buyers don't make decisions based on one interaction. Buyers like to research, compare, talk to colleagues, and often return to vendors long after their first interaction.

68% of B2B buyers already have a front-runner vendor in mind when they begin the purchasing process, and that front-runner wins 80% of the time, according to Forrester.

By the time a prospect reaches out, much of the decision-making has already happened.

You need to influence buyers before they're ready to raise their hand. Focus on building:

• Brand awareness that keeps your company top of mind
• Content that answers questions before buyers talk to sales
• Thought leadership that demonstrates your expertise
• A strong website that helps prospects research independently
• Consistent messaging across every channel and interaction

‍