Learning in the digital era requires educators to be able to develop interactive learning media that students can use anywhere and anytime. The purpose of this research is to develop a math pocket application as an interactive media for online learning that is valid, practical and effective to use. This development research uses the 4D model, namely: define, design, develop and disseminate. However, this development did not reach the disseminate stage due to several limitations of the researcher. The research was carried out for mathematics education students at Universitas Samudra who took basic mathematics courses for the 2020/2021 academic year. The instrument was validated by media experts and material experts. The results showed that the media was very valid with a score of 82.5%, practical with a score of 80%, and very effective with an achievement rate of 93.5%. Therefore, the math pocket application is an interactive media for online learning that is valid, practical and effective in use.