diff --git a/src/backup.sh b/src/backup.sh
index 3a99f80..ddeb430 100755
--- a/src/backup.sh
+++ b/src/backup.sh
@@ -1,17 +1,24 @@
 #!/bin/bash
 
+KEEP_DAILY=${KEEP_DAILY:-6}
+KEEP_WEEKLY=${KEEP_WEEKLY:-3}
+KEEP_MONTHLY=${KEEP_MONTHLY:-48}
+KEEP_YEARLY=${KEEP_YEARLY:-0}
+
 echo "Starting backup script at `date`"
 
 export BORG_RSH='ssh -oBatchMode=yes' # https://borgbackup.readthedocs.io/en/stable/usage/notes.html#ssh-batch-mode
 
+# break any stale locks in case the script was interrupted
 borg break-lock
-borg info
 
+borg info # test whether we have a valid repository
 if [ $? -ne 0 ]; then
     echo "Borg info returned a non-zero status. Initializing Borg..."
     borg init --encryption=repokey
 fi
 
+# the above command will fail if the repo hasn't been already initialized, so we can ignore the return status
 set -e
 
 if [ -d "/snapshot/source" ]; then
@@ -23,8 +30,14 @@ btrfs subvolume snapshot /source /snapshot
 cd /snapshot/source
 borg create --stats --list --filter=AMCE --files-cache=ctime,size --compression=zstd,12 --exclude-from /exclude.conf ::"{hostname}-{now:%Y-%m-%dT%H:%M:%S}" .
 cd -
-borg prune --list --stats --keep-daily=7 --keep-weekly=4 --keep-monthly=12 --keep-yearly=5
-borg compact --threshold=5 --cleanup-commits
+
+borg prune --list --stats \
+    --keep-daily=$KEEP_DAILY \
+    --keep-weekly=$KEEP_WEEKLY \
+    --keep-monthly=$KEEP_MONTHLY \
+    --keep-yearly=$KEEP_YEARLY
+
+borg compact --threshold=5 --cleanup-commits --verbose --progress
 
 btrfs subvolume delete /snapshot/source