Nicotine Clearance Calculator
Nicotine has a plasma half-life of about 2 hours, so most of it is gone within a day and it is down to a fraction of a per cent by 72 hours. Cotinine — what nicotine turns into, and what tests actually look for — has a half-life of about 16 hours and lasts much longer. Enter when you last smoked or vaped and this shows where you are on both curves.
The half-lives are published figures, cited at the foot of the page. This is not a drug-test predictor and it does not claim to be one.
Both default to now. Change them and everything below redraws.
On the 2-hour plasma half-life, the source predicts "persistence of significant levels for 6 to 8 h after cessation of smoking". This is the window in which most people feel the want for the next one.
The first 96 hours
How much is left, hour by hour
| Since your last one | Nicotine (2 h) | Nicotine (11 h) | Cotinine (16 h) |
|---|---|---|---|
| 2 hours | 50% | 88% | 92% |
| 4 hours | 25% | 78% | 84% |
| 8 hours | 6.3% | 60% | 71% |
| 12 hours | 1.6% | 47% | 59% |
| 24 hours | 0.02% | 22% | 35% |
| 48 hours | under 0.01% | 4.9% | 13% |
| 72 hours | under 0.01% | 1.1% | 4.4% |
Percentages are of your own last dose, not of a milligram figure. How much nicotine was in your blood to start with depends on the cigarette, the draw and the day, and no calculator can know it.
The phases
On the 2-hour plasma half-life, the source predicts "persistence of significant levels for 6 to 8 h after cessation of smoking". This is the window in which most people feel the want for the next one.
The NHS puts the harmful carbon monoxide level in your blood at half its starting value after 8 hours, with oxygen levels recovering. Nicotine on the plasma curve is already down to a few per cent of the last dose.
By 24 hours the plasma curve has passed twelve half-lives and the slower terminal curve is at about 22%. The NHS puts carbon monoxide at a non-smoker's level by 48 hours, with the lungs clearing mucus and taste and smell improving.
At 72 hours the terminal curve is at roughly 1% of your last dose. Cotinine, on its 16-hour half-life, is still at about 4% and keeps falling for days after that — which is why a test can still find something when the nicotine has gone.
Past three days the nicotine question is settled. Cotinine is the slow one: in a study of people going through a stop-smoking programme, urinary cotinine was still about 3.4% of its starting level two weeks after the first visit, and 0.2% at eight weeks.
Nicotine mostly gone by 72 hours; cotinine detectable for longer
These are two different substances and most of the confusion online comes from treating them as one. Nicotine is what you took in. Cotinine is what your body turns it into, and it is what nicotine tests almost always measure, because it lasts long enough to be worth measuring.
On the published half-lives, three days is about 36 half-lives of nicotine on the plasma curve and about 6.5 on the slower terminal curve — a fraction of a per cent either way. Cotinine at the same moment is at roughly 4% and falling far more slowly: in one study of a stop-smoking programme, urinary cotinine was still about 3.4% of its starting level two weeks in, and 0.2% at eight weeks.
This page will not tell you whether you will pass a test. That depends on the cut-off used, the sample type, how much you smoked, how quickly you personally metabolise nicotine, and whether you are around other people’s smoke. Anything claiming to predict it is guessing.
Sources
- Benowitz NL, Hukkanen J, Jacob P 3rd. Nicotine Chemistry, Metabolism, Kinetics and Biomarkers. Handbook of Experimental Pharmacology, 2009 The 2-hour plasma half-life, the 11-hour terminal half-life from urinary excretion, and cotinine’s 16-hour half-life.
- Effects of smoking cessation on biological monitoring markers in urine. Genes and Environment, 2020 Urinary cotinine at about 3.4% of baseline two weeks after the first visit and 0.2% at eight weeks.
- NHS Better Health — Quit smoking Carbon monoxide halved at 8 hours and at a non-smoker’s level by 48 hours.
- World Health Organization — Tobacco: Health benefits of smoking cessation Carbon monoxide back to normal at 12 hours, and everything past the first week on the quit smoking timeline.
- Centers for Disease Control and Prevention — Benefits of Quitting Smoking Further reading. No figure on this page is drawn from it.
How the clearance curves are calculated
Exponential decay, three times over: the share of a dose still present is 0.5 raised to the power of the hours elapsed divided by that substance's half-life. Three half-lives are used, all from the same review. Nicotine in plasma: 2 hours. Nicotine's terminal half-life from urinary excretion data: 11 hours. Cotinine, the metabolite that nicotine tests almost always measure: 16 hours. Two curves are drawn for nicotine rather than one because that is what the source reports, and the gap between them is real information rather than an error.
The arithmetic falls out of those numbers. On the 2-hour plasma half-life, a dose is at 25 per cent after 4 hours, about 1.6 per cent after 12 and about 0.02 per cent by 24. Cotinine at 16 hours is still at 35 per cent after 24 hours, 12 per cent after 48 and about 4 per cent after 72 — which is why "how long does nicotine stay in your system" has two very different answers depending on which substance the test is looking for. The table on the page is the same equation at 2, 4, 8, 12, 24, 48 and 72 hours, printed without anything typed in, so the page answers before it is asked.
Every percentage is of your own last dose and not of a milligram figure we invented for you. How much nicotine was in your blood to begin with depends on the cigarette or the device, the draw and the day, and no calculator can know it. Individual clearance also varies with liver enzyme genetics, pregnancy, other medicines and age, so the curves are the published population half-lives rather than a prediction about you. The carbon monoxide lines on the phases below are the NHS's wording, and the two-week cotinine figure is a measured study rather than a projection.
Where these numbers come from
- 1. Nicotine Chemistry, Metabolism, Kinetics and Biomarkers — Benowitz NL, Hukkanen J, Jacob P 3rd, Handbook of Experimental Pharmacology, 2009 (PMC)
- 2. Effects of smoking cessation on biological monitoring markers in urine — Genes and Environment, 2020 (PMC)
- 3. Quit smoking — NHS Better Health
Nothing on this site is medically reviewed. Every figure above was read out of the code that runs on this page, and where a number is our own judgement rather than a published one, the note says so and cites nothing. Method last checked 21 August 2026.
Nicotine and cotinine are two different curves
Two substances, two curves, and most of the confusion online comes from mixing them up. Nicotine is what you took; cotinine is what your liver turns it into, and it is what nicotine tests almost always measure. Nicotine has a plasma half-life of about 2 hours. Cotinine's is about 16. Any page that answers "how long does nicotine stay in your system" with one number has quietly picked one of those two and dropped the other.
This calculator draws both from your own last cigarette or vape, using the half-lives published by Benowitz, Hukkanen and Jacob III, and it draws the nicotine curve twice — once on the 2-hour plasma half-life and once on the 11-hour terminal half-life the same review reports from urinary excretion data. Two curves rather than one because that is what the source says, and the gap between them is real information.
The percentages are of your own last dose, not of a milligram figure we invented for you. How much nicotine was in your blood to begin with depends on the cigarette, the draw and the day, and no calculator can know it.
For what happens to the rest of the body over the same days and beyond, see the quit smoking timeline. The smoke-free days counter keeps the count going after this curve flattens, and the caffeine half-life calculator runs the same arithmetic on a different substance.
Frequently Asked Questions
How long does nicotine stay in your system?
Is nicotine gone after 72 hours?
How long is cotinine detectable?
What is the half-life of nicotine?
Does vaping change the numbers?
Will this tell me whether I will pass a nicotine test?
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