Daily Water Calculator

Water Intake Calculator for Weight Loss

Get your daily water target plus the before-meal plan used in two weight loss trials.

By , Daily Water Calculator

67 to 500 lb

Weight unit

0 to 240

Weather
Meals you will drink before

Enter your weight to see your plan.

Weight in kg × 32.5 mL + 0.6 L per hour of exercise, with 500 mL before meals inside that total

What the research found

Two trials found a modest extra loss with 500 mL of water before meals (adults with obesity, older adults on a reduced-calorie diet). Both were small and short, and both paired water with other help. Water alone wasn't tested.

General information, not medical advice. Medical disclaimerWater isn't a weight loss plan on its own.

What the research found

We looked for a formula that says how much water to drink to lose weight and didn't find one. What exists are trials of a specific habit: drinking 500 mL of water before meals.

  • Adults with obesity, England (Parretti and colleagues, 2015). 84 adults. Everyone got a weight management consultation. One group was also asked to drink 500 mL of water 30 minutes before their main meals, and the other to imagine their stomach was full. After 12 weeks the water group had lost 1.3 kg more (95% confidence interval 0.1 to 2.4 kg). After adjusting for ethnicity, deprivation, age and gender, the difference was 1.2 kg and the interval just crossed zero (P = 0.063). The authors described it as preliminary evidence.
  • Older adults on a diet (Dennis and colleagues, 2010). 48 adults aged 55 to 75 with overweight or obesity, all on a reduced-calorie diet. One group drank 500 mL of water before each daily meal. After 12 weeks, weight loss was about 2 kg greater in the water group.

The Dennis trial also tested a test meal. At the start, a 500 mL drink beforehand lowered calories eaten at that meal (498 versus 541 kcal). At 12 weeks the gap was smaller and not statistically clear (480 versus 506 kcal).

Limits matter here. Both trials were small and ran for 12 weeks. Both gave all participants other weight loss help, so neither tested water on its own. We didn't find long-term follow-up. Read the result as a possible small boost to a plan you're already following, not a reason to drink beyond your target.

How the calculator works

  1. Daily target. The same formula as the main calculator: weight in kilograms times 32.5 mL, plus 0.6 L per hour of exercise. Hot or humid weather uses the top of both ranges. Method and sources are on Water intake formulas compared.
  2. Before-meal water. 500 mL (16.9 fl oz) for each meal you choose, up to three. This is the dose both trials used.
  3. Rest of the day. Your target minus the before-meal water, never below zero.

The before-meal water comes out of your daily target. It doesn't add to it.

Worked example: 200 lb, 30 minutes, typical weather

  1. 200 lb is 90.72 kg, and 90.72 × 32.5 mL = 2,948 mL.
  2. 30 minutes adds 0.5 × 600 = 300 mL. The total, rounded to the nearest 50, is 3,250 mL (110 fl oz).
  3. Three meals with 500 mL each is 1,500 mL (51 fl oz) before meals.
  4. That leaves 1,750 mL (59 fl oz) for the rest of the day.

Press “Try an example” above to load it.

What water will not do

Nothing we read says water alone changes your weight. In the trials, water sat alongside advice or a diet. If you drink well beyond your target hoping for faster results, you add risk without a documented benefit. Our guide on how much water is too much explains how that goes wrong. The trials also leave open who benefits most, so a dietitian or doctor is a better guide for a weight loss plan than a calculator.

When this number does not apply

Talk to a doctor if
  • You're pregnant or breastfeeding.
  • You have a kidney, heart or liver condition.
  • You have been given a fluid limit or a specific drinking target.
  • You take a medication that affects fluids or sodium.
  • This is for a child or teen. The calculator is for adults.

Frequently asked questions

How much water should I drink to lose weight?

We didn't find a separate water formula for weight loss, so this calculator uses the same daily target as the Daily Water Intake Calculator: weight in kilograms times 32.5 mL, plus 0.6 L per hour of exercise. The before-meal plan comes from two trials that used 500 mL.

Does drinking water help you lose weight?

Two randomized trials found modest extra weight loss when people drank 500 mL of water before meals. In both, everyone also got weight management help: a consultation in one, a reduced-calorie diet in the other. The authors of the first trial called their result preliminary evidence. We didn't find a trial that tested water on its own with no other change.

When should I drink the water?

The trial in adults with obesity had people drink 500 mL about 30 minutes before their main meals. The trial in older adults had them drink 500 mL before each daily meal.

Why is the amount 500 mL for everyone?

Both trials used 500 mL, regardless of body size. We didn't find a published adjustment for smaller or larger adults. If 500 mL before each meal is more than your whole daily target, the calculator tells you.

Does a gallon of water a day help with weight loss?

We didn't find a source that supports a gallon as a weight loss method. See Is a gallon of water a day too much? for who a gallon fits.

Does coffee or tea count toward my target?

For most healthy adults, yes. The details are on What counts as water intake.

Is it safe to drink 500 mL before every meal?

Three 500 mL drinks add up to 1.5 liters across a day, which sits inside the daily target for most adults. Spread out, that's a modest amount, and the National Academies didn't set an upper limit for water for healthy people. If you have a fluid limit from your care team, follow that instead.

Sources

  1. Parretti HM, Aveyard P, Blannin A, et al. Efficacy of water preloading before main meals as a strategy for weight loss in primary care patients with obesity: RCT. Obesity 23(9):1785-1791, 2015. PubMed 26237305, DOI 10.1002/oby.21167.
  2. Dennis EA, Dengo AL, Comber DL, et al. Water consumption increases weight loss during a hypocaloric diet intervention in middle-aged and older adults. Obesity 18(2):300-307, 2010. PubMed 19661958, DOI 10.1038/oby.2009.235.
  3. National Academies of Sciences, Engineering, and Medicine. News release, Feb. 11, 2004. Report sets dietary intake levels for water, salt, and potassium to maintain health and reduce chronic disease risk.
  4. Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine & Science in Sports & Exercise 39(2):377-390. PubMed 17277604.

How this page was built. The weight loss water calculator on Daily Water Calculator was built by Cedrick Reese. The daily target uses the same checked formula as the main calculator. The before-meal plan comes from two randomized trials, and we read both abstracts and report their numbers as published, including where a result was no longer clear after adjustment. The 500 mL dose and the three-meal cap are taken from those trials, and nothing here claims more than they showed. We recheck the page when we update the main formula or find new trials. Last reviewed: .

General information for healthy adults, not medical advice. If you are pregnant or breastfeeding, or you have kidney, heart or liver conditions or a fluid limit, ask a clinician first. Terms and medical disclaimer.