diff --git a/src/Mulkup/Ranking.hs b/src/Mulkup/Ranking.hs
new file mode 100644
index 0000000..f162895
--- /dev/null
+++ b/src/Mulkup/Ranking.hs
@@ -0,0 +1,63 @@
+{-# LANGUAGE UndecidableInstances #-}
+
+module Mulkup.Ranking (rankBupItems) where
+
+import qualified Data.List.NonEmpty as NonEmpty
+import qualified Data.Set as Set
+import Data.Time
+import Mulkup.Bupstash
+import Mulkup.Config
+import Mulkup.Prelude
+import Optics
+
+rankBupItems :: TierConfigs -> [BupItem] -> (Set Text, Set Text)
+rankBupItems tierConfigs currentItems =
+  (keepIds, rmIds)
+  where
+    tiers =
+      [ (utctHour . bupItemUTCTime, #hourly),
+        (utctJulianDay . bupItemUTCTime, #daily),
+        (utctWeek . bupItemUTCTime, #weekly),
+        (utctMonth . bupItemUTCTime, #monthly)
+      ]
+
+    keepIds =
+      Set.unions $
+        map
+          ( \(discriminator, cfgLens) ->
+              let tierCfg = tierConfigs ^. cfgLens
+               in tierKeepIds discriminator (tierCfg ^. #keep) currentItems
+          )
+          tiers
+
+    currentIds = Set.fromList (map (^. #id) currentItems)
+    rmIds = Set.difference currentIds keepIds
+
+tierKeepIds :: (BupItem -> Integer) -> Natural -> [BupItem] -> Set Text
+tierKeepIds discriminator keep items =
+  fromList $
+    take (fromIntegral keep) $
+      map (^. #id) $
+        reverse $
+          sortWith bupItemUTCTime $
+            map (head . NonEmpty.sortWith bupItemUTCTime) $
+              elems
+                (groupBy discriminator items :: HashMap Integer (NonEmpty BupItem))
+
+utctHour :: UTCTime -> Integer
+utctHour (UTCTime (ModifiedJulianDay julianDay) tdiff) = (julianDay * 24) + (diffTimeToPicoseconds tdiff `div` (10 ^ (12 :: Integer)) `div` 3600)
+
+utctJulianDay :: UTCTime -> Integer
+utctJulianDay (UTCTime (ModifiedJulianDay julianDay) _) = julianDay
+
+utctWeek :: UTCTime -> Integer
+utctWeek (UTCTime day _) =
+  julianDay + fromIntegral (dayOfWeekDiff (dayOfWeek day) Sunday)
+  where
+    (ModifiedJulianDay julianDay) = day
+    dayOfWeekDiff a b = mod (fromEnum a - fromEnum b) 7
+
+utctMonth :: UTCTime -> Integer
+utctMonth (UTCTime day _) = fromIntegral m
+  where
+    (_, m, _) = toGregorian day