diff --git a/src/NetPresentValue.hs b/src/NetPresentValue.hs
index 5e8b32b4dd231f42d26b3329418c5171fe241318..c8469dad958a002cb9110aa64ef6918a40212627 100644
--- a/src/NetPresentValue.hs
+++ b/src/NetPresentValue.hs
@@ -32,9 +32,16 @@ netPresentValue inputNetPresentValue = foldl (+) 0 pv
     where
         pv = presentValue inputNetPresentValue
 
-presentValue inputNetPresentValue = zipWith (*) (netcashflow income outcome) [0.833, 0.694, 0.579, 0.482, 0.402]
+presentValue inputNetPresentValue = zipWith (*) (netcashflow income outcome) (factorpresentvalue (project_interest inputNetPresentValue))
     where
         income = [income_1 inputNetPresentValue, income_2 inputNetPresentValue, income_3 inputNetPresentValue, income_4 inputNetPresentValue, income_5 inputNetPresentValue]
         outcome = [outcome_1 inputNetPresentValue, outcome_2 inputNetPresentValue, outcome_3 inputNetPresentValue, outcome_4 inputNetPresentValue, outcome_5 inputNetPresentValue]
 
 netcashflow a b = zipWith (-) a b 
+
+power n 1 = n
+power n m = n * (power n (m-1))
+
+powervalue interest n = 1 / (power (1 + interest) n)
+
+factorpresentvalue interest = map (\x -> powervalue interest x) [1..5]