diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,7 @@
+0.0.11
+
+* fix cumulative reporting functions
+
 0.0.10
 
 * split out modules
diff --git a/national-australia-bank.cabal b/national-australia-bank.cabal
--- a/national-australia-bank.cabal
+++ b/national-australia-bank.cabal
@@ -1,5 +1,5 @@
 name:                 national-australia-bank
-version:              0.0.10
+version:              0.0.11
 synopsis:             Functions for National Australia Bank transactions
 description:          Parsing, Processing and other functions for National Australia Bank transactions
 license:              BSD3
diff --git a/src/Data/Bank/NationalAustraliaBank/Report.hs b/src/Data/Bank/NationalAustraliaBank/Report.hs
--- a/src/Data/Bank/NationalAustraliaBank/Report.hs
+++ b/src/Data/Bank/NationalAustraliaBank/Report.hs
@@ -1,7 +1,15 @@
 {-# OPTIONS_GHC -Wall #-}
+{-# LANGUAGE LambdaCase #-}
 
-module Data.Bank.NationalAustraliaBank.Report where
+module Data.Bank.NationalAustraliaBank.Report(
+  cumulativeSumTransactions
+, cumulativeDays
+, cumulativeDays'
+, cumulativePerDay
+, cumulativePerDay'
+) where
 
+import Control.Lens ( view, over, Field1(_1), Field2(_2) )
 import Data.Bank.NationalAustraliaBank.Transaction
     ( Transaction,
       Amount,
@@ -10,42 +18,64 @@
       realAmount,
       date',
       amount' )
+import Data.Bool ( bool )
+import Data.List ( sortOn )
 import Data.Ratio ( Ratio )
 
+withMinimumDate ::
+  (Date -> [a])
+  -> [Transaction]
+  -> [a]
+withMinimumDate _ [] =
+  []
+withMinimumDate f ts@(_:_) =
+  f (minimum (fmap date' ts))
+
+sortedByDateTransactions ::
+  ([(Integer, Transaction)] -> [(Integer, x)])
+  -> [Transaction]
+  -> [x]
+sortedByDateTransactions f ts =
+  let ts' =
+        sortOn (date' . view _2) (zip [0..] ts)
+      r =
+        sortOn (view _1) (f ts')
+  in  fmap (view _2) r
+
 cumulativeSumTransactions ::
   [Transaction]
   -> [Amount]
-cumulativeSumTransactions [] =
-  []
-cumulativeSumTransactions (h:t) =
-  scanl (\a t' -> amount' t' <> a) (amount' h) t
+cumulativeSumTransactions =
+  sortedByDateTransactions
+    (\case
+        [] ->
+          []
+        (n, h):t ->
+          scanl (\(_, a) -> over _2 (\t' -> amount' t' <> a)) (n, amount' h) t
+    )
 
 cumulativeDays ::
   [Transaction]
   -> [Integer]
-cumulativeDays [] =
-  []
-cumulativeDays r@(h:_) =
-  cumulativeDays' (date' h) r
+cumulativeDays ts =
+  withMinimumDate (`cumulativeDays'` ts) ts
 
 cumulativeDays' ::
   Date
   -> [Transaction]
   -> [Integer]
 cumulativeDays' d =
-  fmap (\t -> d `diffDates` date' t + 1)
+  sortedByDateTransactions (fmap (fmap (\t -> date' t `diffDates` d + 1)))
 
 cumulativePerDay ::
   [Transaction]
   -> [Ratio Integer]
-cumulativePerDay [] =
-  []
-cumulativePerDay r@(h:_) =
-  cumulativePerDay' (date' h) r
+cumulativePerDay ts =
+  withMinimumDate (`cumulativePerDay'` ts) ts
 
 cumulativePerDay' ::
   Date
   -> [Transaction]
   -> [Ratio Integer]
 cumulativePerDay' dt txs =
-  zipWith (\a i -> realAmount a / fromInteger i) (cumulativeSumTransactions txs) (cumulativeDays' dt txs)
+  zipWith (\a i -> bool (realAmount a / fromInteger i) 0 (i == 0)) (cumulativeSumTransactions txs) (cumulativeDays' dt txs)