Computing Days Between Dates with bash

Needed a quick way to compute the number of days between two dates:

!/bin/bash
# adapted from https://www.linuxforfreshers.com/2019/01/how-to-count-days-since-specific-date.html
 if [ $# -ne 2 ]; then
     echo "USAGE: $(basename $0) start_date end_date";
     exit 1;
 else
   start=$1;
   end=$2;
   echo "$((($(date +%s --date "$end") - $(date +%s --date "$start"))/(3600*24))) days between $start and $end";
 fi