A 1 rep maximum (1RM) calculator is a tool used in strength training and weightlifting to estimate the maximum amount of weight you can lift for a single repetition in a given exercise. It will take into consideration the number of repetitions performed at a lower weight to predict the maximum weight that can be lifted for one repetition.
These are only estimates and should not be taken as the end-all, be-all. Talk with your provider about steps you can take to get back on track if you aren't already.