diff --git a/prog/pwm/fancontrol b/prog/pwm/fancontrol
index 837e9f93..fcd542f0 100755
--- a/prog/pwm/fancontrol
+++ b/prog/pwm/fancontrol
@@ -141,7 +141,7 @@ function UpdateFanSpeeds {
 		  then pwmval=255 # at specified maxtemp switch to 100%
 		else 
 		  # calculate the new value from temperature and settings
-		  pwmval=`calc "(((${maxt}-${mint})*(${tval}-${mint}))^2*(255-${minso})+${minso})" |cut -d'.' -f1`
+		  pwmval=`calc "(((${tval}-${mint})/(${maxt}-${mint}))^2*(255-${minso})+${minso})" |cut -d'.' -f1`
 		  if [ $pwmpval -eq 0 ]
 		  then # if fan was stopped start it using a safe value
 		  	echo $minsa > $pwmo