Weight Loss Percentage Calculator
Find what percent of your starting weight you've lost — with a dedicated newborn mode that applies the clinical 7–10% birth-weight guidance bands, milestone weights, goal-progress tracking, and a step-by-step breakdown of every number.
Calculator
Worked examples — tap to load
Three common cases. Tap one to load it into the calculator above.
Method & sources
Formula. Weight-loss percentage = (starting weight − current weight) ÷ starting weight × 100. If the result is negative, current weight is above starting weight — the same formula then reads as a weight-gain percentage. Goal progress = (start − current) ÷ (start − goal) × 100.
Adult reference bands. 5–10% of starting weight is the range most widely cited in clinical guidance (e.g. NHLBI obesity treatment guidelines) as associated with measurable health-marker improvements. This is a population reference, not a personal target.
Newborn bands. Typical early loss is 5–10% of birth weight with regain by day 10–14 (WHO). AAP breastfeeding guidance treats loss above 7% of birth weight as warranting a careful feeding assessment. These are educational flags, not a diagnosis — your pediatrician's judgment takes precedence.
Sources: AAP clinical reports on breastfeeding and the healthy newborn; WHO child growth standards; Academy of Breastfeeding Medicine Clinical Protocol #3 (hospital discharge, rev. 2022); NHLBI clinical guidelines on overweight and obesity. Values are educational reference points.
Related calculators
Frequently asked questions
How do you calculate weight loss percentage?
Weight loss percentage = ((starting weight minus current weight) divided by starting weight) times 100. For example, going from 200 lb to 180 lb: (200 - 180) / 200 x 100 = 10% lost.
Is losing 5% of body weight significant?
Yes. A 5 to 10% reduction from starting body weight is the range most widely referenced in clinical guidance (for example the NHLBI obesity treatment guidelines) as associated with measurable improvements in markers like blood pressure and blood sugar. This is a general reference point, not medical advice for your situation.
What is a healthy rate of weight loss?
A commonly cited reference is about 0.5 to 1 kg (1 to 2 lb) per week, which for many adults is roughly 0.5 to 1% of body weight per week. Healthy rates vary with starting weight, medical conditions, and medication. A clinician can advise on what is appropriate for you.
Does it matter if I use pounds or kilograms?
No, the percentage is identical as long as both weights use the same unit. Units cancel out in the division. For example (200-180)/200 = (90.7-81.6)/90.7 = 10%.
How do I calculate weight gain percentage?
Use the same formula. If current weight is above starting weight the result is negative, which this calculator displays as a positive weight-gain percentage. For example, 150 lb to 160 lb is a 6.67% gain relative to the starting weight.
What is the difference between weight loss percentage and goal progress percentage?
Weight loss percentage measures change against your starting weight: (start - current) / start x 100. Goal progress measures how much of your planned journey is done: (start - current) / (start - goal) x 100. For example, starting at 200 lb, now 185 lb, goal 170 lb: you lost 7.5% of starting weight and are 50% of the way to your goal.
How much weight loss is normal for a newborn?
Newborns typically lose 5 to 10% of their birth weight in the first few days as they shed extra fluid, then regain it by day 10 to 14. These are population averages from sources such as the WHO and AAP, not a diagnosis for any individual baby. Always follow your pediatrician's guidance.
When should newborn weight loss be checked by a doctor?
Common clinical reference points: weight loss greater than 7% of birth weight warrants a careful feeding assessment (per AAP breastfeeding guidance); loss above 10% is outside the typical range and should be reviewed promptly with a pediatrician; and birth weight not regained by day 10 to 14 deserves follow-up. Watch wet diapers, feeding frequency, and alertness alongside the number.
How do you calculate newborn weight loss percentage?
Newborn weight loss percentage = ((birth weight minus current weight) divided by birth weight) times 100. For example, a birth weight of 3500 g and current weight of 3255 g is (3500 - 3255) / 3500 x 100 = 7% lost.
I lost more than 5% of my weight without trying. Is that a problem?
Unintentional weight loss greater than about 5% of body weight over 6 to 12 months is generally treated as clinically significant and worth discussing with a clinician, who can look for underlying causes. This tool cannot evaluate causes; it only computes the percentage. Do not ignore persistent unintentional loss.
Should I use BMI or weight loss percentage?
They answer different questions. Weight loss percentage tracks change from your own starting point, which is useful for monitoring progress. BMI compares your current weight to population height-based categories. Many people use both: see our BMI calculator for the BMI number and this tool for progress tracking.
Is this calculator medical advice?
No. This calculator performs arithmetic on numbers you enter. It is for education and personal tracking only and is not medical advice, diagnosis, or treatment. Newborn guidance bands are educational reference points based on published sources and do not replace your pediatrician's judgment.
Free tool by NRTechStudio