Hop ibu different between software

I am using qbrew software for a english ale. With a hop schedule of .5oz of us golden @60min and .25oz @ flameout and .5oz of uk fuggle @ 20min and .25oz @ flame out my ibu was 24.
I downloaded brew assistant to my phone and put my recipe in and came to a ibu of 41. (2.5gal batch btw).

So is one off? I could not see were i made a mistake but i did do a og reading tasted a sample and it taste my like 24ibu on the scale than 41.
so which one is telling me the correct ibu?

Im thinking after puting another recipe in i think it is the brew assisitant app that has the hop ibu off. Everything else reads the same.