Before starting the NHS Choices diet and exercise plan, work out how much weight you need to lose.
Start by using the BMI healthy weight calculator to work out your body mass index (also available as an iPhone app).
Setting a target weight gives you a goal to work towards to keep you focused and motivated while trying to lose weight.
Once you've worked out the weight you want to get to and completion date, download Losing weight - Getting started - our 12-week diet and exercise guide.
Your body mass index (BMI) result tells you if you’re a healthy weight for your height.
If you’re not in the 'healthy weight' range, work out how much you need to lose to be in the healthy range.
Ideally, you should aim for a target weight that gives you a BMI in the healthy weight category (18.5 to 24.9).
If you have lots of weight to lose, then losing enough weight to achieve a healthy BMI may seem pretty daunting.
Instead, you might prefer to set an initial target weight that will improve your health. Losing 5-10% of your current weight has been shown to have significant health benefits.
Some people like to set themselves small weight loss goals to stay motivated as they work their way towards their overall target weight.
Whatever target you set, make sure it is realistic and achievable, otherwise you will set yourself up to fail.
Set a target date
Once you’ve worked out a target weight, you should set a date by which you want to achieve it.
When trying to lose weight, it’s tempting to want fast results. But studies show that people who lose weight too fast end up putting it back on again.
Our weight loss guide is designed to help you lose weight at a safe rate of 0.5kg to 1kg (1lb to 2lb) per week.
Losing weight faster than this, unless under medical supervision, can increase the risk of health problems including malnutrition and gallstones, as well as causing you to feel tired and unwell.
If, for example, you need to lose 10kg (22lbs) to achieve your target weight and you lose weight at a rate of 1kg per week, it will take 10 weeks to lose 10kg.
Write down when you expect to reach your target weight in your diary or somewhere you can see it and use it as a source of motivation.