Beginner Question on IBU

Brewing Processes
1

Brewing with extract and looking at IBU calculations, not sure if I’m doing it right.

6 lbs DME @ 43 ppg boiled with 1.5 gallons.  I have minimal loss, so final boiled volume is within a tenth of starting volume. 
Boiled OG: 1.172?

Hop Schedule:
1 oz 7.1% @ 60 min
1 oz 7.4% @ 20 min
1 oz 6.2% @ 5 min
1 oz 6.2% @ flame out

Plugging that in to brewersfriend I get 67.7 wort IBU, diluted to 5 gallons gives me a final IBU of 19.5.

Does that look like I’m in the ballpark?

2

I would expect closer to 40 IBU. It depends on the actual impact of boil gravity in the concentrated boil. Personally I don’t find there is as much impact as we are led to believe from many of the IBU calculators. But I could be wrong. And likely the correct answer is someplace in between. Taste it at the end and come to your own conclusion.