Hydrogen phosphate or monohydrogen phosphate (systematic name) is the inorganic ion with the formula [HPO4]2-.

Together with dihydrogen phosphate, hydrogenphosphate occurs widely in natural systems.

[1] Most hydrogenphosphate salts are colorless, water soluble, and nontoxic.

It is a conjugate acid of phosphate [PO4]3- and a conjugate base of dihydrogen phosphate [H2PO4]−.

It is formed when a pyrophosphate anion [P2O7]4− reacts with water H2O by hydrolysis, which can give hydrogenphosphate: Hydrogenphosphate is an intermediate in the multistep conversion of phosphoric acid to phosphate: