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diff --git a/src/Model/Date.hs b/src/Model/Date.hs
new file mode 100644
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+++ b/src/Model/Date.hs
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+{-# LANGUAGE DeriveGeneric #-}
+
+module Model.Date where
+
+import GHC.Generics
+import Data.Yaml
+
+data Date = Date
+  { month :: Int
+  , year :: Int
+  } deriving (Show, Read, Eq, Generic)
+
+yearAndMonthDiff :: Date -> Date -> (Int, Int)
+yearAndMonthDiff d1 d2 =
+  let totalMonths = monthDiff d1 d2
+  in  (totalMonths `div` 12, totalMonths `mod` 12)
+
+monthDiff :: Date -> Date -> Int
+monthDiff (Date m1 y1) (Date m2 y2) =
+  if y1 == y2 then
+    1 + abs (m1 - m2)
+  else
+    let (minM, minY, maxM, maxY) =
+          if y1 < y2 then
+            (m1, y1, m2, y2)
+          else
+            (m2, y2, m1, y1)
+    in  12 * (maxY - minY - 1) + (13 - minM) + maxM
+
+instance FromJSON Date