Doing a near Max Takeoff Weight from Dubai to Auckland 16 hr flight taking off from 12R with an OAT of +39 the Takeoff Calculator when set to optimum gives me flaps 2, flex takeoff with packs on.

If I use the calculated numbers I will go off the end of the runway before VR.

I attempted the same takeoff three times using the exact numbers it provided all three times failed takeoffs.

It wasn’t until I removed the flex temp for full TOGA, set Flaps 3 with Packs Off was I able to get off the runway in time.

I think the T/O calculator needs to be looked at.

Yeah I’ve had a similar experience although did make it off out of Sydney (YSSY) for Dubai (OMDB), only 513 tonne but it gave me a flex of 74 and boy oh boy did we use some runway, I’ve never come that close to the end of a runway ever before, it did feel off.

Can confirm, it‘s really Bad!

Flew out of JFK RWY 04L with Head Wind, 24 C Temperaturen, TOW 536T, Flex 56C, Flaps 1+F and straight into the trees

I think, the calculator especially has the Problems with higher weights above 500T!