Typical Adult Dose for Type 2 Diabetes. Immediate-release tablets: 500 milligrams (mg) twice a day, or 850 mg once a day. This dose may be gradually increased by 500 mg a week or 850 mg every two weeks. The maximum daily dose of metformin is 2,550 mg divided into three smaller doses. Extended-release tablets: 500 mg or 1,000 mg daily with an evening meal. The dose can be increased by 500 mg a week to a maximum of 2,000 mg. If you take Fortamet or Glumetza (modified release formulations of metformin), you may be given different dosing instructions.