MFD vs. Calculated MPG

My 2006 prius 'MFD' was right on the money in the beginning, with-in a few tenths. Now, the 'MFD' shows in the low 50's mpg, but when I calculate the numbers, its always in 42/44 mpg range, ALWAYS LATLEY,and I haven't changed my filling up tactics ,when it shuts off, I stop, and most of the time{like 90%} I use the same pump at the same station {Costco} . Its really disappointing, but the numbers don't lie....

 

My 2006 prius 'MFD' was right on the money in the beginning, with-in a few tenths. Now, the 'MFD' shows in the low 50's mpg, but when I calculate the numbers, its always in 42/44 mpg range, ALWAYS LATLEY,and I haven't changed my filling up tactics ,when it shuts off, I stop, and most of the time{like 90%} I use the same pump at the same station {Costco} . Its really disappointing, but the numbers don't lie....

 

confused again, this time it was dead nuts,the MFD was the same ,50.3 both ways,,,,,,,,,,til next time. one thing, I usually fill up no less than a 1/2 tank, however for some reason I got brave and went all the way down to 1 pip, not sure why I waited so long but i did, maybe that has something to do with the differences I 've been seeing/having...

 

In ten months 19196 miles my difference between actual and theoretical is about 3%.
11.9/379. With the theoretical milage slighly higher. My tank differences range from -.95 to +1.25. Which is about a 10% swing.

If my MFD versus actual was much different than what others here are reporting I would:

First be certain of my math
Second, go to my Toyota dealer.

Each tank may vary up to 15% but the long term (six tank minimum) should be under 5%.