According to a new report released today, the best time for mobile application developers to promote or launch a new application across a number of categories tends to be on a weekend, as it turns out. In fact, even if you do well with a weekday release in terms of download numbers, the weekend may be the better time to run an ad campaign that promotes purchases, the report found.

This discovery was based on a three-month study of app revenue and estimated weekly downloads for iOS applications that run January through March of this year.

The study was conducted by San Francisco-based mobile app optimization startup Sensor Tower, which offers an app analytics service that helps developers better understand how to improve their apps’ keywords in order to increase their app’s visibility in app store searches.

The company said it regularly fielded questions from its customers about the timing of new app releases, which actually vary a bit from category to category, and wanted to offer a more comprehensive answer to these questions. The firm broke down downloads and revenue estimates by day for all iOS apps in the U.S. in order to see what percentage of the weekly total took place each day, indicating the best time to launch or run a campaign.

Largely, the data is more relevant to those looking to promote their new applications by running campaigns to attract new users or purchases – something that generally occurs alongside an app’s launch, too. But in some cases, developers may choose to run press about their launch during the week, with the expectation that users will download their app immediately, but may not really begin to engage with it until after work hours or the weekend.

The company found that the best day to run promos varies across the App Store’s different categories. While weekends are often best as a rule of thumb, it seems, there can be some variance when it comes to when to promote purchases versus downloads.

Summarized below are the best days to promote apps across the following top-level App Store categories:

• iOS Books: Sunday (revenue); weekends (downloads)
• Business: Mid-week, e.g. Wed. or Thurs. (revenue); Tues. or Thurs. (downloads)
• Catalogs: Weekends (revenue); Weekends-Monday (downloads)
• Education: Weekends (revenue and downloads)
• Entertainment: Saturday (revenue); Saturday or Sunday (downloads)
• Finance: Sunday (revenue); Weekdays (downloads – users download on weekdays, but play and buy on weekends)
• Food & Drink: Sunday (revenue); Saturday or Sunday (downloads)
• Games: Weekends (revenue and downloads, Sat. is slightly higher)
• Health & Fitness: Weekends, also beginning of week; not Friday (revenue and downloads)
• Lifestyle: Weekends, with small bumps on Mon. and Wed. (revenue and downloads)
• Medical: Wed., Thurs., or Sunday; avoid Saturday (revenue); Sunday (downloads)
• Music: Any day but Tues; explode on Saturday (revenue); Weekends (downloads)
• Navigation: Weekends, followed by Friday (revenue); Weekends only (downloads)
• News: Weekends, avoid Tues. (revenue); Weekends, followed by weekdays (downloads)
• Newsstand: Saturday, avoid Tues. (revenue); Weekends (downloads)
• Photo & Video: Weekends (revenue and downloads)
• Productivity: Any day (revenue and downloads)
• Reference: Weekends, followed by Mon. and Tues. (revenue); Weekends (downloads)
• Social Networking: Weekends (revenue and downloads)
• Sports: Weekends best by far (revenue and downloads)
• Travel: Weekends (revenue and downloads)
• Utilities: Weekends, avoid Tues. (revenue and downloads)
• Weather: Sunday (revenue and downloads)

As you can see by the above list, weekends are generally the best time to promote an app, but there are a few exceptions. Business apps, not too shockingly, do better on weekdays as that’s when most people are in the office or are focused on working. Meanwhile, productivity apps were surprisingly flat across the week, Sensor Tower noted, adding cheekily that “every day is a good day to be productive.”

Medical apps were another exception to the larger rule, with some weekdays being the better days to promote purchases.

However, because a lot of the app categories are focused on leisure activities like dining, travel, reading, music, socializing, shopping and more, it makes sense that users would be looking to discover and buy from these apps more during their downtime – meaning their weekends.