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Adderall Dosage Calculator

Estimate Adderall IR and XR doses by body weight, age group, and dose level using FDA-approved dosing guidelines for ADHD.

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Inputs

Patient Weight

Age Group

Formulation

Dose Level

Estimated Daily Dose

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Estimated Daily Dose—mg/day

The formula

How the
result is
computed.

Adderall Dosage Calculator: Formula and Methodology

Adderall (mixed amphetamine salts) dosing follows a weight-based titration model bounded by FDA-approved age and formulation limits. The calculator estimates a clinically appropriate starting, maintenance, or maximum dose, then caps the result at the regulatory ceiling for the patient's age group and selected formulation.

Core Dosage Formula

The formula is expressed as:

D = min(w × k_level, D_max(age, form)), rounded down to the nearest 2.5 mg increment

This two-part structure first generates a weight-scaled dose and then enforces a hard regulatory ceiling. The calculator returns whichever value is smaller, ensuring no result exceeds FDA-approved limits for the relevant age bracket and formulation.

Formula Variables Explained

w (weight_kg) — Patient body weight in kilograms. Adults typically range 60–100 kg; pediatric patients range from approximately 20–60 kg depending on developmental stage.
k_level (dose coefficient) — A weight-normalized multiplier in mg/kg reflecting the dosing intent. Starting titration uses roughly 0.10–0.15 mg/kg, maintenance dosing uses 0.20–0.30 mg/kg, and the maximum tier approaches 0.40–0.50 mg/kg.
D_max(age, form) — The FDA ceiling dose determined jointly by the patient's age bracket and formulation. Adults on XR: 30 mg/day; adolescents 13–17 on XR: 20 mg/day; children 6–12 on XR: 30 mg/day; patients 6+ on IR: 40 mg/day; children 3–5 on IR: 40 mg/day (rarely approached).

Formulation Differences: IR vs. XR

Adderall IR (immediate-release) begins acting within 30–60 minutes and provides symptom coverage for 4–6 hours, requiring 2–3 daily administrations. Adderall XR (extended-release) delivers medication through a beaded dual-release mechanism, producing therapeutic plasma levels over 10–12 hours and enabling once-daily dosing. According to the FDA Adderall XR Prescribing Information, the XR form is indicated for ADHD in patients aged 6 and older, with dosing initiated at 5–10 mg once daily and titrated upward by 5–10 mg at weekly intervals as needed.

FDA-Approved Dosing Reference by Age Group

Children 6–12 years (XR): Start 5–10 mg once daily; maximum 30 mg/day
Adolescents 13–17 years (XR): Start 10 mg once daily; maximum 20 mg/day
Adults 18+ (XR): Start 20 mg once daily; maximum 30 mg/day
Children 3–5 years (IR): Start 2.5 mg/day; maximum 40 mg/day
Children 6+ (IR): Start 5 mg 1–2 times daily; maximum 40 mg/day

Rounding to 2.5 mg Increments

Adderall IR tablets are commercially available in 5, 7.5, 10, 12.5, 15, 20, and 30 mg strengths. Adderall XR capsules come in 5, 10, 15, 20, 25, and 30 mg strengths. The formula rounds calculated doses down to the nearest 2.5 mg to align with dispensable tablet and capsule sizes, preventing unintentional overshoot on initial fills.

Worked Examples

Example 1 — Pediatric starting dose: A 35 kg child (age 10) beginning Adderall XR: weight-based dose = 35 × 0.14 = 4.9 mg; D_max = 30 mg; min(4.9, 30) = 4.9 mg → rounded to 5.0 mg.

Example 2 — Adult maintenance dose: A 75 kg adult on Adderall XR at maintenance level: weight-based dose = 75 × 0.27 = 20.25 mg; D_max = 30 mg; min(20.25, 30) = 20.25 mg → rounded to 20.0 mg.

Example 3 — Adolescent with dose ceiling: A 90 kg adolescent (age 15) at maximum XR tier: weight-based dose = 90 × 0.45 = 40.5 mg; D_max (age 13–17, XR) = 20 mg; min(40.5, 20) = 20.0 mg — the age ceiling overrides the weight calculation.

Clinical Basis and Limitations

Weight-adjusted amphetamine titration is supported by peer-reviewed evidence. A systematic review published in PMC (Cortese et al., 2018) confirms that titrated amphetamine therapy starting at the lowest effective dose and increasing in 5–10 mg weekly steps achieves optimal ADHD symptom control with a favorable safety profile. The Oregon Health & Science University Drug Class Review on Pharmacologic Treatments for ADHD further validates weight-based dosing as an appropriate initial framework in pediatric populations. This calculator produces educational estimates only. A licensed prescriber must determine the actual dose through clinical evaluation, review of comorbidities, and ongoing monitoring of response and adverse effects.

Reference

Frequently asked questions

What is the standard starting dose of Adderall for adults?

The FDA-approved starting dose of Adderall XR for adults is 20 mg once daily. For Adderall IR, adults typically begin at 5 mg once or twice daily. Prescribers increase the dose by 5 to 10 mg at weekly intervals based on therapeutic response and tolerability, up to a maximum of 30 mg per day for XR formulations.

How is Adderall dosage calculated based on body weight?

Adderall dosing uses a weight-normalized coefficient in mg/kg multiplied by the patient's body weight in kilograms. Starting titration applies approximately 0.10 to 0.15 mg/kg, while maintenance dosing uses 0.20 to 0.30 mg/kg. The calculated result is capped at the FDA maximum for the patient's age group and formulation, then rounded down to the nearest 2.5 mg dispensable tablet increment.

What is the maximum daily dose of Adderall approved by the FDA?

Maximum daily doses differ by formulation and age group. Adderall XR for adults and children aged 6 to 12 is capped at 30 mg per day. Adolescents aged 13 to 17 on XR are limited to 20 mg per day. Adderall IR carries a 40 mg per day ceiling for patients aged 6 and older. Exceeding these limits increases cardiovascular and neurological risk without evidence of additional therapeutic benefit.

What is the difference between Adderall IR and XR dosing schedules?

Adderall IR is immediate-release, active within 30 to 60 minutes and lasting 4 to 6 hours, typically requiring 2 to 3 daily administrations. Adderall XR uses extended-release bead technology to deliver medication over 10 to 12 hours via a bimodal release curve, allowing a single morning dose. The dosage calculator applies separate FDA ceilings for each formulation because XR and IR carry different approved maximum doses for adolescent age groups.

How often should Adderall dosage be adjusted during titration?

Clinical guidelines recommend increasing Adderall dosage by 5 to 10 mg no more frequently than once per week, allowing sufficient time to assess therapeutic effect and adverse events such as appetite suppression, elevated heart rate, or sleep disturbance. Research reviewed in the OHSU Drug Class Review on ADHD Pharmacotherapy supports this weekly titration cadence as the safest approach to reaching an effective maintenance dose while minimizing stimulant-related side effects.

Is this Adderall dosage calculator appropriate for children?

The calculator supports pediatric dosing using FDA-approved age brackets beginning at age 3 for IR formulations and age 6 for XR formulations. It applies age-specific and formulation-specific dose ceilings to keep all calculated values within regulatory limits. However, any pediatric Adderall dose must be prescribed and monitored by a licensed healthcare provider who can evaluate the child's weight, cardiovascular health, developmental status, and individual response to stimulant medication.