Parents who start their back-to-school shopping earlier in the summer tend to spend more money overall, according to a recent survey by Deloitte.

Overall, the survey found that 62% of respondents plan to start shopping before August. Those shoppers spend an average of $544 on back-to-school purchases. By comparison, respondents who begin later, in August or September, spend an average of $455.

Many early shoppers (66%) said they plan to shop at different points throughout the summer to take advantage of deals, and 40% expect to find the best back-to-school deals early on in the season. 

It’s worth noting that Deloitte didn’t delve into why late shoppers held off on back-to-school shopping. Since 37% said they belong to a household with income below $50,000, it may simply be a matter of economics for many, or a determination that lower prices are likely to be had later in the season.

There’s no true consensus on when the back-to-school season begins. Amazon’s July shopping holiday Amazon Prime Day has become something of a marker for retailers and consumers alike.

In a 2017 AYTM Market Research survey, 42.6% of US internet users said they planned to start back-to-school shopping by the end of July. And a May 2018 survey by RetailMeNot found that 84% of US retailers think the season begins before or on Amazon Prime Day.

A Cardlytics study found that even though nearly three-quarters of back-to-school shoppers bought school items only in-store in 2017, Prime Day had the effect of shifting shoppers’ spend ahead by nearly one month.