Track your weight loss rate and clinical severity over time
This calculator provides estimates only. Consult your GP or a healthcare professional for personalised advice.
Tracking your body weight loss as a percentage over a specific time period is essential for understanding whether your weight loss rate is safe and sustainable. While losing weight through a calorie deficit is generally positive for those who are overweight, losing it too quickly can lead to muscle loss, nutritional deficiencies, gallstones, and other health complications. The NHS and NICE guidelines emphasise that the rate of loss matters just as much as the total amount lost. This calculator goes beyond simple percentage calculations by incorporating clinical severity bands based on your weekly loss rate. It tells you whether you are losing weight at a safe pace (under 1% of body weight per week), a moderate pace that needs monitoring (1-1.5% per week), or a rapid pace that warrants medical review (over 1.5% per week). It also flags if your total loss exceeds 10% of your starting weight, which is a threshold that the NHS considers significant enough to warrant a GP consultation. Whether you are following a structured diet plan, recovering from illness, or monitoring a patient, this tool provides the clinical context that raw numbers alone cannot offer.
To use this calculator: 1. Enter your starting weight in kilograms. If you know your weight in stones, multiply by 6.35 to convert. For example, 13 stone 5 pounds = (13 x 6.35) + (5 x 0.454) = 85 kg approximately. 2. Enter your current weight in kilograms. 3. Enter the time period in weeks over which the weight was lost. For example, if you started dieting 6 weeks ago, enter 6. 4. Review your results: - Total percentage of body weight lost - Total weight lost in kilograms - Weekly loss rate in kg per week and percentage per week - Clinical severity assessment 5. The bar chart compares your weekly loss rate against the safe threshold (0.5 kg/week) and maximum recommended threshold (1.0 kg/week). 6. If the severity assessment indicates rapid loss or significant total loss, consider speaking to your GP or a registered dietitian.
The calculations are as follows: Total Loss (kg) = Starting Weight - Current Weight Percentage Lost = (Total Loss / Starting Weight) x 100 Weekly Loss (kg/week) = Total Loss / Number of Weeks Weekly Loss (% per week) = Percentage Lost / Number of Weeks For example, if you weighed 85 kg four weeks ago and now weigh 78 kg: Total Loss = 85 - 78 = 7 kg Percentage Lost = (7 / 85) x 100 = 8.2% Weekly Loss = 7 / 4 = 1.75 kg/week Weekly Loss = 8.2% / 4 = 2.05% per week The clinical severity bands are based on the weekly percentage rate: - Under 1% per week: Safe rate of loss - 1% to 1.5% per week: Moderate, monitor closely for side effects - Over 1.5% per week: Rapid loss, medical review recommended Additionally, if total loss exceeds 10% of starting weight, this is flagged regardless of the weekly rate, as the NHS considers this level of loss significant enough to warrant clinical attention.
Inputs: Starting Weight: 85 kg, Current Weight: 78 kg, Time Period: 4 weeks
Inputs: Starting Weight: 90 kg, Current Weight: 88 kg, Time Period: 8 weeks
Inputs: Starting Weight: 100 kg, Current Weight: 85 kg, Time Period: 20 weeks
This calculator is intended for adults aged 18 and over. Unintentional weight loss (losing weight without trying) at any rate should be discussed with your GP, as it can indicate underlying health conditions such as thyroid disorders, diabetes, or other medical issues. For intentional weight loss, the NHS recommends combining a balanced diet with regular physical activity for the best long-term outcomes.