The reality is, your body starts healing itself within a few days of your last cigarette. Cigarettes contain a lot of harmful chemicals which affect every organ in your body - the obvious ones being your lungs and heart.
When you stub out that last cigarette, within just 20 minutes your heart rate will start to normalise again and 48 hours later, your body will have expelled any carbon monoxide too. The first three days are typically the most difficult for people to quit because of these reasons. The cravings peak around the 48 - 72 hour mark, so if you can push through those you’re already doing great.
After that three day mark, your breathing will start to improve. Even the little things like getting to the top of the staircase in your house will be easier. You might also notice a bit of coughing - don’t worry, it’s all for the good. Your body will start to expel debris that’s been sitting in your lungs meaning more space for fresh air to fuel your body.
Once you get towards the end of your 28 day period, your heart will be happier too. Blood will pump more freely - long story short, less stitches and leg cramps and way more energy¹.
Aside from all of that, smoking is expensive. Even if you’re a moderate smoker getting through a 10 pack a day, you still stand to save around £2000 a year by leaving them behind.