Co-Star: astrology-as-social-app bet grows to 4.9M MAU, then sells to Midjourney

Co-Star is a mobile astrology app founded in New York in 2017 by Banu Guler, Anna Kopp and Ben Weitzman and launched on 2017-10-17. Users enter birth time and place; the app pulls planetary positions from NASA Jet Propulsion Laboratory data and layers on birth charts, daily horoscopes and compatibility reads written by AI plus human astrologers. Guler, previously a fashion-industry product and design director, has said the idea began with a hand-made, book-length birth-chart gift that convinced her astrology could move beyond a niche audience.

The bet was that astrology could sell as an aesthetic, social product: a magazine-like black-and-white UI, one blunt notification a day ('do not text your ex'), and no attempt to buy attention. That design was the growth engine - users screenshotted the sharp daily horoscopes and posted them on Instagram and Reddit - and Co-Star reached ~4.3-4.9M monthly active users and about 200K downloads a month on a near-zero ad budget.

The weak point was monetization. BaijIng, citing DianDian data, put monthly post-store revenue near $400-500K for most of the year, with a one-off December 2025 spike toward $1M from an $11.99 annual forecast product; the Pro Star subscription contributed under 10% of revenue, and one-time purchases like $2.99 chart reads dominated. Midjourney, in its first acquisition, bought Co-Star's parent in a deal that closed in spring 2026 and was announced on 2026-07-24; terms were undisclosed, Guler became chief design officer, and the ~24-person team joined.

As of 2026-09-02 Co-Star still operates as an app inside Midjourney under Guler's direction, while she also builds the design, product and front-end team for Midjourney's first standalone apps. The week after the announcement, 39 of 46 new App Store reviews were one-star, most citing AI, Midjourney or data concerns, while downloads rose about 16% and revenue only 6.4% (kchuhai) - a reminder that the audience that loved Co-Star's mystique did not all welcome its new owner.