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Nicotine Clearance Calculator

Enter when you last smoked. See live countdowns to CO clearance (12h), nicotine clearance (72h), and your current phase.

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What's Happening Inside Your Body

The 12-Hour CO Clearance

Carbon monoxide from cigarette smoke binds to haemoglobin 200 times more strongly than oxygen, forming carboxyhaemoglobin. This directly reduces your blood's oxygen-carrying capacity — essentially creating mild chronic hypoxia. Within 12 hours of quitting, your CO levels normalise and blood oxygen returns to normal, improving energy and reducing cardiovascular strain.

The 72-Hour Nicotine Clearance

Nicotine has a biological half-life of approximately 2 hours. Its primary metabolite, cotinine, has a half-life of roughly 16 hours. Within 72 hours, nicotine and its immediate metabolites are effectively cleared from the bloodstream. This is why the 48–72 hour window is the hardest: receptors in your brain are maximally starved. After 72 hours, the brain begins downregulating receptor density, and the acute physical pull weakens.

Why Phases Matter

Understanding which phase you are in removes the fear of the unknown. Just Smoked means nicotine is still active. CO Clearing means your blood oxygen is improving. Nicotine Clearing is the hardest phase — peak withdrawal — but it is time-limited. Almost Clear is the final stretch. Cleared means the acute pharmacological chapter is closed.

Frequently Asked Questions

How long does nicotine stay in your system?
Nicotine itself has a half-life of about 2 hours, meaning it largely clears the bloodstream within 72 hours. However, cotinine — a metabolite of nicotine — can remain detectable in urine for 3–4 days (up to 3 weeks in heavy smokers). The cravings driven by nicotine receptor sensitisation typically peak at 48–72 hours and begin easing after 3 days.
Why does carbon monoxide clear faster than nicotine?
Carbon monoxide (CO) binds to haemoglobin and is expelled through normal respiration. Your lungs process it continuously, so CO levels normalise within 12 hours of your last cigarette. Nicotine, by contrast, is fat-soluble and undergoes hepatic metabolism — a slower enzymatic process.
Why are cravings worst at 48–72 hours?
Nicotine occupies acetylcholine receptors in the brain. When nicotine is absent, those receptors are hypersensitised and signal for more. Nicotine levels hit near-zero around 72 hours, which coincides with peak receptor demand. After that, the brain begins downregulating receptor density and cravings become less intense.
Will I feel better after 72 hours?
Physically, yes — the acute nicotine withdrawal is largely over. Most ex-smokers report clearer breathing, improved smell and taste, and reduced physical cravings by day 3–4. Psychological cravings (triggered by habits and associations) continue for weeks but are manageable.
Does the phase label mean I'm fully healed?
The phases track nicotine and CO clearance specifically. Lung and cardiovascular recovery continues for months and years — this calculator focuses on the first 72 hours which are the most physiologically intense.

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