How long can you keep an open can of formula? IF I keep the unused formula in the freezer, can I use it 2-3 months later?

so far for my kids, when they r using formula, i leave it on the table, away from sunlight, and they can use about 2-3 months. this is in particular for my eldest gal of age 8 as i will normally buy the 1.8kg tin and she drinks only twice a day.