Isotretinoin (Accutane) Dose Calculator
Enter your body weight, daily dose, and treatment duration to calculate your isotretinoin cumulative dose in mg/kg and see how close you are to the evidence-based 150-220 mg/kg target. Switch between metric and imperial weight, flip to duration-solve or daily-dose-solve mode, and check the reference table for standard dosing benchmarks. Results update as you type.
What is cumulative dose and why does it matter?
Isotretinoin treatment is not measured only by how many milligrams you take per day but by how much medication your body receives relative to its weight over the entire course. That total exposure is called the cumulative dose, expressed in mg/kg. It matters because the lasting effects of isotretinoin - clearing acne and keeping it clear - depend on total exposure, not just daily dose. A 2025 JAMA Dermatology retrospective cohort study of 19,907 patients found that each additional mg/kg of cumulative dose was associated with roughly a 0.4% lower relapse rate (HR 0.996) and about a 1% lower rate of needing a second course (HR 0.99). In that study relapse occurred in 26.1% of patients below 120 mg/kg, 19.8% between 120 and 220 mg/kg, and 22.2% above 220 mg/kg, so the benefit does not continue past roughly 220 mg/kg. That is why dermatologists commonly aim for a target in the 150-220 mg/kg band rather than stopping at the older 120 mg/kg minimum.
How to calculate your isotretinoin cumulative dose
The formula is straightforward: cumulative dose (mg/kg) = (daily dose in mg x number of days) divided by body weight in kg. For example, a patient weighing 70 kg taking 40 mg per day for 20 weeks (140 days) accumulates 40 x 140 = 5,600 mg total, which divided by 70 kg gives 80 mg/kg - well below the evidence-based 150 mg/kg minimum. The same patient would need roughly 37 weeks at 40 mg/day to reach 150 mg/kg. Alternatively, 80 mg/day for 20 weeks gives 160 mg/kg. This calculator handles all three solve modes: compute cumulative dose from daily dose and duration, compute the duration needed to reach a target at a given dose, or compute the daily dose needed to hit a target within a planned duration.
Understanding daily dose ranges and side effects
Dermatologists typically start isotretinoin at a lower dose such as 0.5 mg/kg/day to assess tolerability before increasing to 1.0 mg/kg/day. Higher doses (up to 2.0 mg/kg/day) may be used for severe nodular acne but increase the risk and intensity of side effects - dry lips, dry skin, nosebleeds, joint pain, and elevated liver enzymes and lipids (which are monitored with blood tests). The key insight from recent research is that the final cumulative dose matters more than how fast you get there. A slow titration reaching 150-220 mg/kg achieves outcomes comparable to a faster course that hits the same total exposure. The calculator shows your daily dose in mg/kg/day alongside the cumulative figure so you can see both dimensions at once.
Capsule sizes and practical dosing
Isotretinoin (sold as Accutane and many generics) is available in 10 mg, 20 mg, 30 mg, and 40 mg capsules in most markets. Doses must be taken with food because isotretinoin is fat-soluble and absorption roughly doubles when taken with a high-fat meal. Common daily doses are 20 mg, 40 mg, 60 mg, and 80 mg, often split as two doses per day. Your prescriber will determine the starting dose based on your weight, severity of acne, and likely tolerability. This calculator does not recommend a specific dose - enter the dose your dermatologist prescribed to track your cumulative progress.
Standard isotretinoin dosing benchmarks
| Parameter | Standard value | Clinical significance |
|---|---|---|
| Daily dose | 0.5-1.0 mg/kg/day | Standard prescribing range |
| Daily dose (severe acne) | Up to 2.0 mg/kg/day | Maximum for nodular/severe cases |
| Traditional cumulative target | 120-150 mg/kg | Older guideline minimum |
| Evidence-based minimum | 150 mg/kg | Recommended minimum to reduce relapse |
| Optimal cumulative range | 150-220 mg/kg | Lowest relapse rate observed in the 120-220 mg/kg band (JAMA Derm 2025) |
| Typical treatment duration | 15-20 weeks (FDA label) | 16-24 weeks is common in practice |
| Available capsule strengths | 10 mg, 20 mg, 30 mg, 40 mg | Common Accutane strengths |
| Relapse risk reduction | ~0.4% per additional mg/kg | HR 0.996 per mg/kg, JAMA Dermatology 2025 cohort study |
Standard clinical parameters for isotretinoin therapy. Individual prescriptions vary - follow your dermatologist's guidance.
Frequently asked questions
What is the recommended cumulative dose for isotretinoin?
Most dermatologists target a cumulative dose in the 150-220 mg/kg range. The older guideline minimum was 120 mg/kg, but a 2025 JAMA Dermatology cohort study of 19,907 patients found relapse was less common in the 120-220 mg/kg band (19.8%) than below 120 mg/kg (26.1%), with no further benefit above 220 mg/kg (22.2%). Note that the FDA label itself specifies 0.5-1 mg/kg/day for 15-20 weeks and does not state a cumulative target, so the target is a clinical convention rather than a labelled requirement. Your dermatologist decides when to stop.
How long does a typical isotretinoin course last?
Most courses run 16-24 weeks (4-6 months) at a standard dose of 0.5-1.0 mg/kg/day. The exact duration depends on your daily dose and body weight - a lower daily dose or higher body weight requires more weeks to reach the target cumulative dose. This calculator can solve for duration given your daily dose, weight, and target cumulative dose.
Does a higher daily dose mean a shorter course?
Generally yes, but the total cumulative dose still needs to be reached. A higher daily dose gets you to the target faster - for instance, 80 mg/day for a 70 kg person reaches 150 mg/kg in about 19 weeks, whereas 40 mg/day takes about 37 weeks. However, higher daily doses also increase the risk and severity of side effects, so the approach is tailored individually.
What happens if my cumulative dose is below 120 mg/kg?
A cumulative dose below 120 mg/kg is generally considered insufficient for durable clearance. Acne relapse rates are substantially higher after short or low-dose courses. If treatment is stopped early, a dermatologist may recommend restarting a new course once all monitoring criteria are met. You should not stop treatment without consulting your prescriber.
Is isotretinoin the same as Accutane?
Yes. Accutane was the original brand name for isotretinoin. The Roche patent expired and Accutane was withdrawn from the US market in 2009. Since then, multiple generics have been approved (Claravis, Amnesteem, Myorisan, Absorica, and others). All contain isotretinoin as the active ingredient and are used at the same dosing targets.
Can I use this calculator to determine my dose?
No. This calculator is a reference and tracking tool. Only a licensed dermatologist or other prescribing clinician can determine the right dose for your body weight, severity of acne, blood test results, other medications, and overall health. Isotretinoin is a teratogen and requires strict monitoring including pregnancy testing for patients who can become pregnant.
Why is food important when taking isotretinoin?
Isotretinoin is fat-soluble, meaning it is absorbed much better when taken with a fatty meal. Studies have shown absorption can nearly double compared to taking it on an empty stomach. Most prescribers advise taking capsules with the largest meal of the day. Some newer formulations (like Absorica LD) use absorption-enhancing technology that reduces the food requirement, but most generics still benefit significantly from co-administration with food.
Sources
- Isotretinoin capsules - FDA prescribing information (DailyMed). Dosage and Administration: 0.5-1 mg/kg/day in two divided doses for 15-20 weeks, up to 2 mg/kg/day in very severe disease.
- Lai J, Barbieri JS. Acne Relapse and Isotretinoin Retrial in Patients With Acne. JAMA Dermatology, 2025;161(4):367-374. (Retrospective cohort, 19,907 patients)
- Layton AM. Optimal management of acne to prevent scarring and psychological sequelae. American Journal of Clinical Dermatology, 2001;2(3):135-141.