diff --git a/src/ac/ed/lurg/country/gams/TauCalculationManager.java b/src/ac/ed/lurg/country/gams/TauCalculationManager.java
index a56f6ef75c694c291c2ebb242667f608e6b317bf..05879e5bdadc6560603720baea294909f209c3f3 100644
--- a/src/ac/ed/lurg/country/gams/TauCalculationManager.java
+++ b/src/ac/ed/lurg/country/gams/TauCalculationManager.java
@@ -39,7 +39,7 @@ public class TauCalculationManager {
 		double tau;
 
 		if(year > ModelConfig.DIET_CHANGE_START_YEAR && year < ModelConfig.DIET_CHANGE_END_YEAR)
-			tau = initialTau + ((ModelConfig.DIET_CHANGE_START_YEAR - year) * (shiftTau - initialTau) / (ModelConfig.DIET_CHANGE_END_YEAR- ModelConfig.DIET_CHANGE_START_YEAR));  //  interpolation
+			tau = initialTau + ((year - ModelConfig.DIET_CHANGE_START_YEAR) * (shiftTau - initialTau) / (ModelConfig.DIET_CHANGE_END_YEAR- ModelConfig.DIET_CHANGE_START_YEAR));  //  interpolation
 		else if (year >= ModelConfig.DIET_CHANGE_END_YEAR)
 			tau = shiftTau; 
 		else