It does, in fact, take inflation into account. As well as purchasing power parity (PPP) across countries.
"And making sure everyone's making at least $1.25 a day isn't the end of the fight either. The world's median income is still only $3 to $4 a day. By comparison, the poverty line in the US for a family of four is $16.61 per person per day. Once under-$1.25-a-day poverty is eradicated, the world needs to set about eradicating under-$15-a-day poverty, which will be a substantially harder task."