Revenue retained, divided by total revenue form the previous time period [1] [2]
[1] Net Dollar Retention vs. Net Revenue Retention - VC Adventure. Retrieved May 21, 2021, from https://sethlevine.com/archives/2021/03/net-dollar-retention-vs-net-revenue-retention.html
[2] Retrieved May 21, 2021, from https://medium.com/@kunaljasty/why-net-dollar-retention-is-the-most-important-saas-metric-to-track-db29aa66fa0b
[3] Aktas, M. What is Net Dollar Retention and How to Calculate It?. Retrieved May 21, 2021, from https://userguiding.com/blog/net-dollar-retention-ndr/