⚠️ CLINICAL SAFETY NOTICE: This metformin dosage calculator is for EDUCATIONAL purposes only. Always verify dosing with current FDA labeling and clinical guidelines. Metformin is contraindicated in eGFR <30 mL/min/1.73m². Hold before iodinated contrast or surgery and restart only after 48 hours with stable renal function.
⚠️ Educational only. Verify with current FDA labeling and clinical guidelines.
📌 Quick Answer: Metformin is started at 500 mg once or twice daily with meals and titrated by 500 mg weekly to a usual maintenance dose of 1000-2000 mg/day. Max dose is 2550 mg/day (IR) or 2000 mg/day (ER). eGFR 45-59: max 2000 mg/day. eGFR 30-44: max 1000 mg/day. eGFR <30: contraindicated.
📋 Key Takeaways — Metformin Dosing at a Glance
Starting dose: 500 mg once or twice daily with meals
Titrate: Increase by 500 mg/week as tolerated
Usual maintenance: 1000-2000 mg/day in divided doses
Max dose (normal renal function): 2550 mg/day (IR) or 2000 mg/day (ER)
eGFR 45-59: Max 2000 mg/day, do not initiate
eGFR 30-44: Max 1000 mg/day, do not initiate
eGFR <30: CONTRAINDICATED
Hold before contrast/surgery; restart after 48h with stable renal function
ℹ️ Over 40,000 clinicians use this metformin dosage calculator 2026. Get starting dose, titration schedule, and eGFR-based max dose for T2DM, PCOS, and prediabetes.
💡 GI Tolerability Tip: Start low, go slow. Take with meals. Consider ER formulation if GI side effects occur.
📊 Metformin Dosing by eGFR — 2026 FDA/ADA Guidelines
eGFR (mL/min/1.73m²)
Max Daily Dose
Initiation
Monitoring
≥60
2550 mg (IR) / 2000 mg (ER)
Yes
Annual eGFR
45-59
2000 mg
Do not initiate
Every 3-6 months
30-44
1000 mg (half max)
Do not initiate
Every 3 months
<30
Contraindicated
No
—
👨 Patient A — New T2DM Diagnosis
eGFR: 75 | Age: 52 | Formulation: IR
Result: Start 500 mg BID with meals. Titrate to 1000 mg BID over 2-4 weeks. Max 2550 mg/day.
✅ "Standard titration. No renal adjustment needed."
👩 Patient B — CKD Stage 3b
eGFR: 38 | Age: 68 | Formulation: ER
Result: Do not initiate. If already on metformin, reduce to max 1000 mg/day. Monitor eGFR every 3 months.
⚠️ "High lactic acidosis risk. Consider alternative or dose reduction."
What is a Metformin Dosage Calculator and How Does It Work?
A metformin dosage calculator is a clinical tool that helps healthcare providers determine the appropriate starting dose, titration schedule, and maximum daily dose of metformin based on the patient's renal function (eGFR) and indication. Our metformin dosage calculator 2026 uses FDA labeling and ADA Standards of Care to provide eGFR-adjusted dosing for type 2 diabetes, PCOS (off-label), and prediabetes (off-label). The calculator also flags contraindications and provides titration guidance to minimize GI side effects.
How does the metformin dosing calculator work? Enter the indication, eGFR, patient age, formulation (IR or ER), current dose, and any GI intolerance or planned contrast/surgery. The metformin dose calculator instantly shows the recommended starting dose, titration schedule, eGFR-adjusted max dose, target maintenance dose, formulation recommendation, and safety status.
Metformin Starting Dose and Titration (2026)
Adults (T2DM): Start 500 mg once or twice daily with meals. Increase by 500 mg per week as tolerated until glycemic goals are met or max dose reached. Usual maintenance: 1000-2000 mg/day in divided doses. Max: 2550 mg/day (IR) or 2000 mg/day (ER).
Children (10-16 years, T2DM): Start 500 mg once or twice daily with meals. Max 2000 mg/day in divided doses.
PCOS (off-label): Start 500 mg once or twice daily, titrate to 1500-2000 mg/day in divided doses. ER formulation often preferred for tolerability.
eGFR-Based Dosing Adjustments (Critical Safety)
eGFR ≥60: No adjustment. Max 2550 mg/day (IR) or 2000 mg/day (ER).
eGFR 45-59: Do not initiate metformin. If already on therapy, max 2000 mg/day. Reassess risk/benefit. Monitor eGFR every 3-6 months.
eGFR 30-44: Do not initiate. If already on therapy, reduce dose by 50% (max 1000 mg/day). Monitor eGFR every 3 months.
eGFR <30:Contraindicated. Discontinue metformin. Risk of lactic acidosis.
When to Hold Metformin (Contrast, Surgery, Illness)
Iodinated contrast: Hold metformin at the time of contrast administration. Restart only after 48 hours and confirmed stable renal function.
Surgery: Hold metformin at the time of surgery with general, spinal, or epidural anesthesia. Restart no earlier than 48 hours post-surgery or resumption of oral nutrition, with stable renal function.
Acute illness: Hold during dehydration, severe infection, shock, or any condition that may impair renal function.
Managing GI Side Effects
GI side effects (diarrhea, nausea, abdominal discomfort) occur in 20-30% of patients starting metformin. Strategies: start low (500 mg daily), titrate slowly (weekly), take with meals, and consider switching to extended-release (ER) formulation. ER metformin significantly reduces GI intolerance in most patients.
Vitamin B12 Monitoring
Long-term metformin use reduces vitamin B12 levels. Monitor B12 periodically, especially with long duration, high dose, or symptoms of deficiency (anemia, neuropathy). Supplement if deficient.
❓ Frequently Asked Questions
How is metformin dosed for type 2 diabetes?
Start with 500 mg once or twice daily with meals. Titrate by 500 mg weekly as tolerated. Typical maintenance dose is 1000-2000 mg/day. Max daily dose is 2550 mg (US) or 2000 mg (ER). Use our metformin dosage calculator for eGFR-adjusted dosing.
What is the max metformin dose based on eGFR?
eGFR ≥60: Max 2550 mg/day. eGFR 45-59: Max 2000 mg/day, do not initiate. eGFR 30-44: Max 1000 mg/day, do not initiate. eGFR <30: Contraindicated.
How do you titrate metformin to avoid GI side effects?
Start low (500 mg daily) and increase by 500 mg per week as tolerated. Take with meals. Extended-release (ER) formulation may reduce GI side effects.
What is the metformin dose for PCOS?
Off-label PCOS dosing: Start 500 mg once or twice daily, titrate to 1500-2000 mg/day in divided doses. ER formulation is often preferred for tolerability.
Can children take metformin?
Yes, metformin is approved for children 10 years and older with type 2 diabetes. Start 500 mg once or twice daily with meals. Max 2000 mg/day in divided doses.
When should metformin be held before contrast or surgery?
Hold metformin at the time of iodinated contrast or surgery. Restart only after 48 hours and confirmed stable renal function.
💡 Expert Tips for Metformin Dosing
Tip #1: Always check eGFR before starting metformin and at least annually. For eGFR 45-59, do not initiate; for 30-44, reduce dose by 50%.
Tip #2: Start low and go slow. 500 mg once daily for 1-2 weeks, then increase to twice daily if tolerated. Weekly 500 mg increments.
Tip #3: Take with meals to reduce GI upset. If intolerance persists, switch to ER formulation before abandoning metformin.
Tip #4: Hold metformin before contrast or surgery. Restart after 48 hours only with stable renal function.
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🛡️ CDCalculators proprietary metformin dosage calculator 2026 — data sources: FDA labeling, ADA Standards of Care 2026, KDIGO guidelines. Last updated October 17, 2026. Disclaimer: Educational purposes only. Always verify with current prescribing information and clinical judgment.