Adderall Dosage Calculator
This calculator looks up the FDA-approved Adderall starting dose, weekly titration step, and maximum daily dose based on your age group, the condition being treated, and whether you use immediate-release (IR) or extended-release (XR) tablets. It also shows how many doses to take per day, how long each dose lasts, and how long the drug takes to clear your system based on its half-life. Results follow the prescribing information and authoritative clinical guidelines; they are for general education only and do not replace your prescriber's instructions.
What is Adderall and how is it dosed?
Adderall is a combination of amphetamine salts (75% dextroamphetamine, 25% levoamphetamine) used to treat attention-deficit/hyperactivity disorder (ADHD) and narcolepsy. It works by increasing the release and blocking the reuptake of dopamine and norepinephrine in the brain, improving focus, impulse control, and wakefulness. Dosing always starts at the lowest effective amount and is increased gradually, a process called titration, until the desired clinical effect is achieved or side effects limit further increases. There is no single correct dose; the right amount varies considerably between individuals based on metabolism, weight, age, and individual response.
Immediate-release vs. extended-release
Adderall IR (immediate-release) tablets are absorbed rapidly and begin working within 15-30 minutes. Effects last approximately 4-6 hours, so most patients take two or three doses spread across the morning and early afternoon. Adderall XR (extended-release) capsules use a biphasic delivery system: half the contents are released immediately and the other half are released roughly four hours later. This extends the coverage to 10-12 hours from a single morning dose, reducing the need for midday dosing at school or work. XR is generally preferred when once-daily dosing improves adherence. Neither form should be taken late in the day because of its stimulant effects on sleep.
Understanding titration and the maximum dose
Starting at the minimum dose and increasing slowly (weekly is the standard schedule) allows the prescriber to find the lowest dose that controls symptoms. For adults with ADHD on IR, the starting dose is 5 mg and steps are 5 mg per week up to a ceiling of 40 mg per day. Research shows that doses above 40 mg/day for ADHD rarely produce additional therapeutic benefit and increase cardiovascular side effects, appetite suppression, and anxiety. For narcolepsy the ceiling is higher (60 mg/day) because the mechanism of benefit is different. Maximum doses in the reference table represent absolute upper limits, not targets; many patients achieve full symptom control well below them.
Half-life and clearance
The half-life of Adderall IR averages about 9-14 hours (commonly cited as approximately 11.5 hours); XR has a similar but slightly longer effective half-life of around 12 hours due to its biphasic release. After five half-lives (roughly 57 hours for IR or 60 hours for XR) about 97% of a single dose has been eliminated from the body. This matters for several reasons: it determines how long side effects persist, how early a missed dose can be taken, how long before a drug test the medication will be detectable, and how quickly levels fall if someone needs to stop. Urine drug screens can detect amphetamines for approximately two to four days after the last dose in most people.
FDA-recommended Adderall dosing by age and indication
| Age group | Indication | Form | Starting dose | Titration step | Max/day |
|---|---|---|---|---|---|
| 3-5 years | ADHD | IR only | 2.5 mg | +2.5 mg/week | 40 mg |
| 6-12 years | ADHD | IR | 5 mg | +5 mg/week | 40 mg |
| 6-12 years | ADHD | XR | 5 mg | +5 mg/week | 30 mg |
| 13-17 years | ADHD | IR | 5 mg | +5 mg/week | 40 mg |
| 13-17 years | ADHD | XR | 10 mg | +10 mg after 1 wk | 20 mg |
| Adults (18+) | ADHD | IR | 5 mg | +5 mg/week | 40 mg |
| Adults (18+) | ADHD | XR | 20 mg | +5 mg/week | 40 mg |
| 6-11 years | Narcolepsy | IR only | 5 mg | +5 mg/week | 60 mg |
| 12-17 years | Narcolepsy | IR only | 10 mg | +10 mg/week | 60 mg |
| Adults (18+) | Narcolepsy | IR only | 10 mg | +10 mg/week | 60 mg |
Starting doses, titration steps, and daily maximums from the FDA prescribing information. XR = Adderall XR (extended-release); IR = immediate-release. All doses in mg.
Frequently asked questions
What is the typical starting dose of Adderall for adults with ADHD?
For adults with ADHD, the FDA-recommended starting dose is 5 mg once or twice daily for immediate-release, or 20 mg once daily for extended-release. The dose is then increased in 5 mg increments each week based on response and tolerability, up to a maximum of 40 mg per day.
How does Adderall XR differ from regular Adderall in dosing?
Adderall XR (extended-release) is taken once daily in the morning, while immediate-release tablets are usually taken two or three times a day. For adults, XR typically starts at 20 mg and has the same 40 mg daily ceiling as IR. The advantage of XR is that a single capsule covers most of the waking day, but it cannot be split or crushed - if a lower dose is needed, you need to switch to a different capsule strength.
What is the maximum safe dose of Adderall?
The FDA-approved maximum for ADHD in adults and most age groups is 40 mg per day. For narcolepsy the approved maximum is 60 mg per day. These are hard ceilings from clinical trial data; studies have not demonstrated meaningful additional benefit at higher doses, while the risk of cardiovascular effects, anxiety, and dependence increases. Any dose above 40 mg for ADHD should be a decision made in close consultation with a prescriber.
How long does Adderall stay in your system?
The half-life of Adderall is approximately 9-14 hours. After five half-lives - about 57-70 hours from a single dose - roughly 97% of the drug has been cleared from the bloodstream. Urine drug tests can detect amphetamines for two to four days after the last dose for most people. Detection windows are longer with heavy or prolonged use, and shorter in people with faster metabolism or high urine pH.
Is Adderall dosing different for children than adults?
Yes. For children aged 3-5 with ADHD, the starting dose is lower at 2.5 mg per day because younger children are more sensitive to stimulants. Children aged 6-12 start at 5 mg. Adolescents aged 13-17 using Adderall XR start at 10 mg. Adults start at 5 mg (IR) or 20 mg (XR). In all cases the principle is the same: start low, increase slowly, and use the lowest dose that controls symptoms.
Can Adderall XR be used for narcolepsy?
No. Adderall XR does not have FDA approval for narcolepsy. The immediate-release formulation is used for narcolepsy, typically starting at 5-10 mg daily and titrated upward by 5-10 mg per week, with a maximum of 60 mg per day divided into two or three doses.
What happens if I miss a dose of Adderall?
If you miss a morning dose, you can take it as soon as you remember if it is still early in the day. If it is close to the afternoon or evening, skip the missed dose - taking it late risks insomnia. Never double up to compensate for a missed dose. Because of Adderall's stimulant effects on sleep, prescribers generally recommend taking the last dose of the day no later than early afternoon.