{"id":1052,"date":"2026-10-18T13:26:55","date_gmt":"2026-10-18T13:26:55","guid":{"rendered":"https:\/\/bmicalculatornhs.co.uk\/?page_id=1052"},"modified":"2026-11-13T05:06:50","modified_gmt":"2026-11-13T05:06:50","slug":"bmi-formula-explained-with-examples","status":"publish","type":"page","link":"https:\/\/bmicalculatornhs.co.uk\/blog\/bmi-formula-explained-with-examples\/","title":{"rendered":"BMI Formula Explained | Examples & NHS BMI Calculation"},"content":{"rendered":"
\n
\n
\n <\/p>\n
\u00f0\u009f\u0093\u0085 Published 6 April 2026 \u00a0\u00c2\u00b7\u00a0 Reflects current NHS & CDC 2026 guidelines<\/div>\n

<\/p>\n

What Is BMI and Why Does It Matter in 2026?<\/h2>\n

\n Body Mass Index (BMI) remains one of the most widely used screening tools in healthcare worldwide in 2026.
\n Used by NHS GPs, CDC public health researchers, and clinicians globally, BMI provides a quick numerical
\n estimate of whether a person’s body weight is proportionate to their height \u00e2\u0080\u0094 and whether they may be at
\n increased health risk as a result.\n <\/p>\n

\n While BMI has limitations \u00e2\u0080\u0094 it does not directly measure body fat, and it can misclassify muscular
\n individuals or certain ethnic groups \u00e2\u0080\u0094 it remains the foundational first step in weight assessment.
\n Understanding the BMI formula<\/strong> and how to interpret it is essential for anyone following
\n NHS or CDC weight loss guidelines in 2026.\n <\/p>\n

\n

\u00e2\u009c\u0085 2026 NHS definition:<\/strong> BMI is a screening tool \u00e2\u0080\u0094 not a diagnostic measure. It is calculated from height and weight, and interpreted alongside waist circumference, ethnicity, age, and clinical assessment for a complete picture of health.<\/p>\n<\/p><\/div>\n

<\/p>\n

The BMI Formula \u00e2\u0080\u0094 Metric and Imperial<\/h2>\n

\n The BMI formula is straightforward. There are two versions depending on whether you are using
\n metric or imperial measurements:\n <\/p>\n

<\/p>\n

\n
\u00f0\u009f\u0087\u00ac\u00f0\u009f\u0087\u00a7 Metric Formula (Used by NHS)<\/div>\n
BMI = Weight (kg) \u00c3\u00b7 Height (m)\u00c2\u00b2<\/div>\n
Height must be in metres<\/strong>, not centimetres. Convert: 175 cm = 1.75 m<\/div>\n
<\/div>\n
\u00f0\u009f\u0087\u00ba\u00f0\u009f\u0087\u00b8 Imperial Formula (Used by CDC)<\/div>\n
BMI = (Weight in lbs \u00c3\u0097 703) \u00c3\u00b7 Height (inches)\u00c2\u00b2<\/div>\n
Or: divide weight in pounds by height in inches squared, then multiply by 703<\/div>\n<\/p><\/div>\n

\n Both formulas produce the same numerical result \u00e2\u0080\u0094 the metric version is simply more intuitive for
\n UK users following NHS guidelines. The key point is that height must be squared<\/strong>
\n (multiplied by itself) before dividing weight. This is the step most people miss when calculating
\n manually.\n <\/p>\n

<\/p>\n

How to Calculate BMI Step by Step<\/h2>\n

\n Here is a step-by-step breakdown of the metric BMI calculation \u00e2\u0080\u0094 the method used by the NHS
\n and recommended for UK adults in 2026:\n <\/p>\n

\n

\u00f0\u009f\u0093\u0090 Step-by-Step Metric BMI Calculation<\/h4>\n
\n
1<\/div>\n
Convert height to metres.<\/strong> If your height is in centimetres, divide by 100. Example: 175 cm \u00c3\u00b7 100 = 1.75 m<\/code><\/div>\n<\/p><\/div>\n
\n
2<\/div>\n
Square your height.<\/strong> Multiply your height in metres by itself. Example: 1.75 \u00c3\u0097 1.75 = 3.0625<\/code><\/div>\n<\/p><\/div>\n
\n
3<\/div>\n
Divide your weight by the result.<\/strong> Weight in kg divided by height squared. Example: 75 \u00c3\u00b7 3.0625 = 24.5<\/code><\/div>\n<\/p><\/div>\n
\n
4<\/div>\n
Interpret your result.<\/strong> Compare your BMI to the NHS categories below. A result of 24.5<\/code> falls in the healthy weight range (18.5\u00e2\u0080\u009324.9).<\/div>\n<\/p><\/div>\n<\/p><\/div>\n

<\/p>\n

BMI Formula: 4 Real-World Examples<\/h2>\n

\n Let us work through four real examples covering different heights, weights, and BMI outcomes.
\n Each uses the NHS metric formula and is mapped to the current 2026 NHS BMI categories:\n <\/p>\n

\n
\n
\u00f0\u009f\u0091\u00a9 Example 1 \u00e2\u0080\u0094 Healthy Weight<\/div>\n
Weight: 65 kg<\/strong><\/div>\n
Height: 1.68 m<\/strong> (168 cm)<\/div>\n
65 \u00c3\u00b7 (1.68 \u00c3\u0097 1.68)
= 65 \u00c3\u00b7 2.8224
= 23.0<\/strong><\/div>\n
BMI: 23.0<\/div>\n
\u00e2\u009c\u0085 Healthy Weight (18.5\u00e2\u0080\u009324.9)<\/div>\n<\/p><\/div>\n
\n
\u00f0\u009f\u0091\u00a8 Example 2 \u00e2\u0080\u0094 Overweight<\/div>\n
Weight: 95 kg<\/strong><\/div>\n
Height: 1.80 m<\/strong> (180 cm)<\/div>\n
95 \u00c3\u00b7 (1.80 \u00c3\u0097 1.80)
= 95 \u00c3\u00b7 3.24
= 29.3<\/strong><\/div>\n
BMI: 29.3<\/div>\n
\u00e2\u009a\u00a0\u00ef\u00b8\u008f Overweight (25\u00e2\u0080\u009329.9)<\/div>\n<\/p><\/div>\n
\n
\u00f0\u009f\u0091\u00a9 Example 3 \u00e2\u0080\u0094 Obese Class I<\/div>\n
Weight: 90 kg<\/strong><\/div>\n
Height: 1.62 m<\/strong> (162 cm)<\/div>\n
90 \u00c3\u00b7 (1.62 \u00c3\u0097 1.62)
= 90 \u00c3\u00b7 2.6244
= 34.3<\/strong><\/div>\n
BMI: 34.3<\/div>\n
\u00f0\u009f\u0094\u00b4 Obese Class I (30\u00e2\u0080\u009334.9)<\/div>\n<\/p><\/div>\n
\n
\u00f0\u009f\u0091\u00a8 Example 4 \u00e2\u0080\u0094 Underweight<\/div>\n
Weight: 55 kg<\/strong><\/div>\n
Height: 1.82 m<\/strong> (182 cm)<\/div>\n
55 \u00c3\u00b7 (1.82 \u00c3\u0097 1.82)
= 55 \u00c3\u00b7 3.3124
= 16.6<\/strong><\/div>\n
BMI: 16.6<\/div>\n
\u00f0\u009f\u009f\u00a3 Underweight (Below 18.5)<\/div>\n<\/p><\/div>\n<\/p><\/div>\n

\n Rather than calculating manually, you can use our free
\n Visual BMI Calculator<\/a>
\n to get your NHS-aligned BMI result instantly \u00e2\u0080\u0094 with a visual body shape illustration and full
\n category interpretation. For children, the
\n Child Growth Chart Calculator UK<\/a>
\n uses age- and gender-adjusted NHS charts rather than adult BMI, which is the correct approach
\n for under-18s.\n <\/p>\n

<\/p>\n

NHS BMI Categories 2026 \u00e2\u0080\u0094 What Your Number Means<\/h2>\n

\n Once you have calculated your BMI, you need to interpret it using the current 2026 NHS BMI
\n categories. These thresholds are unchanged from previous years and remain the standard used
\n by NHS GPs and healthcare professionals across the UK:\n <\/p>\n\n\n\n\n\n\n\n\n\n\n
BMI Range<\/th>\nNHS Category<\/th>\nWhat This Means<\/th>\n<\/tr>\n<\/thead>\n
Below 18.5<\/strong><\/td>\n<\/span>Underweight<\/td>\nMay indicate insufficient nutrition or an underlying health condition. GP advice recommended.<\/td>\n<\/tr>\n
18.5 \u00e2\u0080\u0093 24.9<\/strong><\/td>\n<\/span>Healthy Weight \u00e2\u009c\u0093<\/td>\nThe NHS-recommended healthy weight range for most UK adults. Maintain through balanced diet and activity.<\/td>\n<\/tr>\n
25 \u00e2\u0080\u0093 29.9<\/strong><\/td>\n<\/span>Overweight<\/td>\nSlightly above healthy range. Weight loss of 0.5\u00e2\u0080\u00931 kg per week recommended through lifestyle changes.<\/td>\n<\/tr>\n
30 \u00e2\u0080\u0093 34.9<\/strong><\/td>\n<\/span>Obese Class I<\/td>\nAssociated with increased health risks. NHS weight management support strongly recommended.<\/td>\n<\/tr>\n
35 \u00e2\u0080\u0093 39.9<\/strong><\/td>\n<\/span>Obese Class II<\/td>\nSignificant health risks. Medical support likely needed. GP referral advised.<\/td>\n<\/tr>\n
40 and above<\/strong><\/td>\n<\/span>Obese Class III<\/td>\nSevere health risks. Immediate medical attention recommended. Bariatric options may be considered.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\n Important for 2026:<\/strong> The NHS continues to apply lower BMI thresholds for people
\n from South Asian, Chinese, Black, and other ethnic minority backgrounds, for whom health risks
\n may be elevated at lower BMI values. If you are of South Asian heritage, the NHS recommends
\n considering overweight from BMI 23 and obese from BMI 27.5.\n <\/p>\n

\n Find your healthy weight target range using our
\n Ideal Weight Calculator UK<\/a>.\n <\/p>\n

<\/p>\n

Safe Weight Loss Per Week: NHS vs CDC Guidelines 2026<\/h2>\n

\n Once you know your BMI, the next step \u00e2\u0080\u0094 if your BMI is above 25 \u00e2\u0080\u0094 is to understand the
\n recommended safe rate of weight loss<\/strong>. Both NHS and CDC weight loss guidelines
\n in 2026 are consistent on this point, and consistent with all previous years:
\n 0.5 to 1 kg (1 to 2 lbs) per week<\/strong>.\n <\/p>\n

\n

\u00e2\u009c\u0085 2026 NHS & CDC consensus:<\/strong> The safe rate of weight loss per week 0.5\u00e2\u0080\u00931 kg<\/strong> remains the globally recommended standard, endorsed by NHS, CDC, and WHO. This rate is achievable through a daily calorie deficit of 500\u00e2\u0080\u00931,000 kcal via a balanced diet and 150+ minutes of moderate exercise weekly.<\/p>\n<\/p><\/div>\n

\n This figure is not arbitrary. One kilogram of body fat contains approximately 7,700 kilocalories.
\n To lose 0.5 kg per week requires burning 550 kcal more per day than consumed; to lose 1 kg per
\n week requires a daily deficit of approximately 1,100 kcal. Both are physiologically achievable
\n without risking muscle loss, nutritional deficiency, or hormonal disruption.\n <\/p>\n\n\n\n\n\n\n\n\n
Authority<\/th>\n2026 Safe Weekly Rate<\/th>\nDaily Deficit Target<\/th>\nExercise Minimum<\/th>\n<\/tr>\n<\/thead>\n
\u00f0\u009f\u0087\u00ac\u00f0\u009f\u0087\u00a7 NHS<\/strong><\/td>\n0.5\u00e2\u0080\u00931 kg<\/td>\n500\u00e2\u0080\u00931,000 kcal\/day<\/td>\n150 min\/week moderate<\/td>\n<\/tr>\n
\u00f0\u009f\u0087\u00ba\u00f0\u009f\u0087\u00b8 CDC<\/strong><\/td>\n0.45\u00e2\u0080\u00930.9 kg (1\u00e2\u0080\u00932 lbs)<\/td>\n500\u00e2\u0080\u0093750 kcal\/day<\/td>\n150\u00e2\u0080\u0093300 min\/week<\/td>\n<\/tr>\n
\u00f0\u009f\u008c\u008d WHO<\/strong><\/td>\n0.5\u00e2\u0080\u00931 kg<\/td>\n500\u00e2\u0080\u00931,000 kcal\/day<\/td>\n150+ min\/week<\/td>\n<\/tr>\n
\u00e2\u009a\u00a0\u00ef\u00b8\u008f Rapid loss<\/strong><\/td>\nAbove 1.5 kg\/week<\/td>\n1,650+ kcal deficit<\/td>\nNot a safe substitute<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\n For a full side-by-side breakdown, read our dedicated article on
\n NHS vs CDC weight loss guidelines explained<\/a>,
\n and our deep-dive into the
\n 0.5\u00e2\u0080\u00931 kg weight loss rule explained<\/a>.\n <\/p>\n

<\/p>\n

Why Slow Weight Loss Outperforms Rapid Loss<\/h2>\n

\n The 2026 NHS and CDC position on gradual weight loss is backed by a growing body of long-term
\n outcome data. Here is why the safe weight loss per week NHS CDC<\/strong> recommendation
\n of 0.5\u00e2\u0080\u00931 kg consistently outperforms faster approaches:\n <\/p>\n

Preserves Lean Muscle Mass<\/h3>\n

\n At a 500\u00e2\u0080\u00931,000 kcal daily deficit, the body draws primarily on stored fat. At larger deficits,
\n it increasingly breaks down muscle protein, lowering the basal metabolic rate. This is the
\n primary biological reason crash dieters regain weight: their metabolism has been slowed by
\n the loss of metabolically active muscle tissue.\n <\/p>\n

Maintains Hormonal Balance<\/h3>\n

\n Gradual weight loss preserves more stable leptin (fullness) and ghrelin (hunger) levels.
\n Crash diets trigger a sharp hormonal rebound \u00e2\u0080\u0094 intense hunger that outlasts the diet itself
\n and is the main driver of yo-yo weight cycles, recognised as a serious health concern in 2026.\n <\/p>\n

Ensures Nutritional Adequacy<\/h3>\n

\n At 1,400\u00e2\u0080\u00931,800 kcal per day (the range that typically produces a 500\u00e2\u0080\u00931,000 kcal deficit),
\n a varied, balanced diet can meet all essential micronutrient requirements. Crash diets routinely
\n fail this test, causing deficiencies in iron, vitamin D, B12, calcium, zinc, and folate.\n <\/p>\n

Builds Permanent Habits<\/h3>\n

\n Achieving 0.5\u00e2\u0080\u00931 kg per week over several months requires real, sustainable behavioural change \u00e2\u0080\u0094
\n the kind that becomes ingrained as daily habit rather than temporary restriction. This is the
\n foundation of the NHS’s long-term weight management approach, unchanged in 2026.\n <\/p>\n

<\/p>\n

Risks of Rapid Weight Loss in 2026<\/h2>\n

\n NHS and CDC guidelines in 2026 continue to warn explicitly against exceeding the 0.5\u00e2\u0080\u00931 kg
\n per week threshold without medical supervision. The risks are clinically documented and include:\n <\/p>\n

\n

\n \u00e2\u009a\u00a0\u00ef\u00b8\u008f Documented risks of rapid weight loss (NHS & CDC 2026):<\/strong> Gallstone formation
\n triggered by rapid fat mobilisation; significant lean muscle and bone density loss; severe
\n fatigue, cognitive impairment, and mood disorders; hair thinning (telogen effluvium);
\n dangerous electrolyte imbalances including hypokalemia and hyponatremia; deficiencies in
\n iron, vitamin B12, folate, calcium, and vitamin D; menstrual irregularity and fertility
\n impacts in women; and dramatically elevated long-term weight regain risk.\n <\/p>\n<\/p><\/div>\n

\n For more on this topic, see our complete guides:
\n safe rate of weight loss per week<\/a>
\n and how much weight can you lose per week safely<\/a>.\n <\/p>\n

<\/p>\n

6 Tips to Lose Weight Safely in 2026<\/h2>\n

\n Following the 2026 NHS and CDC weight loss guidelines means applying the same evidence-based
\n principles that have been refined over decades. Here are the most effective strategies:\n <\/p>\n

\n
\u00f0\u009f\u00a5\u0097<\/div>\n
\n

Follow the NHS Eatwell Guide<\/h4>\n

Build meals around half-plate vegetables, a quarter lean protein, and a quarter wholegrains. Reduce ultra-processed foods, added sugar, and high-saturated-fat products. This naturally produces the 500\u00e2\u0080\u0093750 kcal deficit recommended by NHS and CDC guidelines without calorie obsession.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n

\n
\u00f0\u009f\u009a\u00b6<\/div>\n
\n

Move 150+ Minutes Per Week<\/h4>\n

Both NHS and CDC recommend 150 minutes of moderate aerobic activity weekly as a minimum \u00e2\u0080\u0094 brisk walking, swimming, cycling, or dancing. In 2026, NHS services increasingly recommend strength training alongside cardio to preserve muscle mass during weight loss.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n

\n
\u00f0\u009f\u0093\u008a<\/div>\n
\n

Track BMI Monthly, Not Just Weight<\/h4>\n

Daily body weight fluctuates by 1\u00e2\u0080\u00932 kg due to water retention, salt, hormones, and digestion. Use our Visual BMI Calculator<\/a> monthly to track genuine category-level progress \u00e2\u0080\u0094 a more medically meaningful measure than the scale alone.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n

\n
\u00f0\u009f\u0098\u00b4<\/div>\n
\n

Protect Your Sleep \u00e2\u0080\u0094 7 to 9 Hours<\/h4>\n

In 2026, sleep is firmly established as a key pillar of weight management. Adults sleeping under 6 hours per night show elevated ghrelin and reduced leptin, consuming on average 300\u00e2\u0080\u0093500 kcal more the following day. Seven to nine hours nightly is the NHS and CDC recommendation.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n

\n
\u00f0\u009f\u0092\u00a7<\/div>\n
\n

Hydrate Before Meals<\/h4>\n

Drinking 500 ml of water 30 minutes before a meal has been shown to reduce meal calorie intake by an average of 13%. Adequate hydration (6\u00e2\u0080\u00938 glasses\/day per NHS guidelines) also reduces thirst-hunger confusion that leads to unnecessary snacking.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n

\n
\u00f0\u009f\u00a9\u00ba<\/div>\n
\n

Use NHS Services for BMI 30+<\/h4>\n

UK adults with BMI above 30 may access free NHS weight management programmes, including dietary support, behavioural therapy, and in appropriate cases, anti-obesity medication or bariatric surgery referral. Speak to your GP in 2026 \u00e2\u0080\u0094 NHS support significantly improves long-term outcomes. For children’s growth tracking alongside adult programmes, use our Percentile Calculator UK<\/a> and Baby Weight Percentile Calculator UK<\/a>.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n

\n

\n \u00f0\u009f\u0092\u00a1 Tools for the whole family in 2026:<\/strong> Our
\n Child Growth Chart Calculator UK<\/a>
\n and Percentile Calculator UK<\/a>
\n use current NHS growth chart data for children aged 0\u00e2\u0080\u009318. The
\n Baby Weight Percentile Calculator UK<\/a>
\n tracks infant growth from birth to 2 years. All tools are free, NHS-aligned, and updated for 2026.\n <\/p>\n<\/p><\/div>\n

<\/p>\n

\n

Frequently Asked Questions<\/h2>\n
\n