diff --git a/src/backup.rs b/src/backup.rs
index 6a18f39b..4d6fd55f 100644
--- a/src/backup.rs
+++ b/src/backup.rs
@@ -179,6 +179,9 @@ pub use dynamic_index::*;
 mod backup_info;
 pub use backup_info::*;
 
+mod prune;
+pub use prune::*;
+
 mod datastore;
 pub use datastore::*;
 
diff --git a/src/backup/prune.rs b/src/backup/prune.rs
new file mode 100644
index 00000000..758890f6
--- /dev/null
+++ b/src/backup/prune.rs
@@ -0,0 +1,122 @@
+use failure::*;
+use std::collections::{HashMap, HashSet};
+use std::path::PathBuf;
+
+use chrono::{DateTime, Datelike, Local};
+
+use super::{BackupDir, BackupInfo};
+
+enum PruneMark { Keep, Remove }
+
+fn mark_selections<F: Fn(DateTime<Local>, &BackupInfo) -> String> (
+    mark: &mut HashMap<PathBuf, PruneMark>,
+    list: &Vec<BackupInfo>,
+    keep: usize,
+    select_id: F,
+) {
+
+    let mut include_hash = HashSet::new();
+
+    let mut already_included = HashSet::new();
+    for info in list {
+        let backup_id = info.backup_dir.relative_path();
+        if let Some(PruneMark::Keep) = mark.get(&backup_id) {
+            let local_time = info.backup_dir.backup_time().with_timezone(&Local);
+            let sel_id: String = select_id(local_time, &info);
+            already_included.insert(sel_id);
+        }
+    }
+
+    for info in list {
+        let backup_id = info.backup_dir.relative_path();
+        if let Some(_) = mark.get(&backup_id) { continue; }
+        let local_time = info.backup_dir.backup_time().with_timezone(&Local);
+        let sel_id: String = select_id(local_time, &info);
+
+        if already_included.contains(&sel_id) { continue; }
+
+        if !include_hash.contains(&sel_id) {
+            if include_hash.len() >= keep { break; }
+            include_hash.insert(sel_id);
+            mark.insert(backup_id, PruneMark::Keep);
+        } else {
+            mark.insert(backup_id, PruneMark::Remove);
+        }
+    }
+}
+
+pub fn compute_prune_info(
+    mut list: Vec<BackupInfo>,
+    keep_last: Option<u64>,
+    keep_daily: Option<u64>,
+    keep_weekly: Option<u64>,
+    keep_monthly: Option<u64>,
+    keep_yearly: Option<u64>,
+) -> Result<Vec<(BackupInfo, bool)>, Error> {
+
+    let mut mark = HashMap::new();
+
+    BackupInfo::sort_list(&mut list, false);
+
+    // remove inclomplete snapshots
+    let mut keep_unfinished = true;
+    for info in list.iter() {
+        // backup is considered unfinished if there is no manifest
+        if info.files.iter().any(|name| name == super::MANIFEST_BLOB_NAME) {
+            // There is a new finished backup, so there is no need
+            // to keep older unfinished backups.
+            keep_unfinished = false;
+        } else {
+            let backup_id = info.backup_dir.relative_path();
+            if keep_unfinished { // keep first unfinished
+                mark.insert(backup_id, PruneMark::Keep);
+            } else {
+                mark.insert(backup_id, PruneMark::Remove);
+            }
+            keep_unfinished = false;
+        }
+    }
+
+    if let Some(keep_last) = keep_last {
+        mark_selections(&mut mark, &list, keep_last as usize, |_local_time, info| {
+            BackupDir::backup_time_to_string(info.backup_dir.backup_time())
+        });
+    }
+
+    if let Some(keep_daily) = keep_daily {
+        mark_selections(&mut mark, &list, keep_daily as usize, |local_time, _info| {
+            format!("{}/{}/{}", local_time.year(), local_time.month(), local_time.day())
+        });
+    }
+
+    if let Some(keep_weekly) = keep_weekly {
+        mark_selections(&mut mark, &list, keep_weekly as usize, |local_time, _info| {
+            format!("{}/{}", local_time.year(), local_time.iso_week().week())
+        });
+    }
+
+    if let Some(keep_monthly) = keep_monthly {
+        mark_selections(&mut mark, &list, keep_monthly as usize, |local_time, _info| {
+            format!("{}/{}", local_time.year(), local_time.month())
+        });
+    }
+
+    if let Some(keep_yearly) = keep_yearly {
+        mark_selections(&mut mark, &list, keep_yearly as usize, |local_time, _info| {
+            format!("{}/{}", local_time.year(), local_time.year())
+        });
+    }
+
+    let prune_info: Vec<(BackupInfo, bool)> = list.into_iter()
+        .map(|info| {
+            let backup_id = info.backup_dir.relative_path();
+            let keep = match mark.get(&backup_id) {
+                Some(PruneMark::Keep) => true,
+                _ => false,
+            };
+            (info, keep)
+        })
+        .collect();
+
+    Ok(prune_info)
+}