Average Facebook ad clickthrough rates are highest on weekends and lowest on Monday, according to new research by TBG Digital.

Specifically, Saturday’s average CTR is 12 percent higher than average CTR on Monday. Advertisers can use this information to understand their own campaign performance and perhaps adjust their Facebook ad strategies.

Facebook ad clickthrough rate is closely tied to cost per click and cost per impression. Ads with higher CTR are generally served more frequently. When ads have lower CTR, advertisers typically have to increase their bid price to get the same number of impressions. Facebook advertisers who want to maximize the CTR of their ads might decide to shift campaigns to the weekend when the averages seem to be in their favor.

TBG Digital CEO Simon Mansell says the daily differences in CTR are likely related to supply and demand, as well as changes in how people use Facebook through the week. When there is more traffic on Facebook, but the same number of advertisers running ads, the frequency of ads shown per person may increase. Higher frequency general results in lower CTR.

Another possibility is that users who visit Facebook on Monday and other weekdays are more focused on browsing News Feed or friends’ photos, perhaps because they’re checking Facebook on breaks between work or school. This would lead users to look at ads less or be less likely to click away from what they’re doing. On weekends, users are more likely to be looking at Facebook in their downtime and could be more susceptible to ads.

London-based marketing and technology company TBG Digital, which specializes in Facebook advertising, looked at clickthrough rates over 66 billion impressions from January to March. The company did not provide actual values for CTR by day, but says that the chart above is to scale.