What water can and can't do for weight loss
Water is not a fat burner, and any calculator that promises otherwise is selling something. What the evidence does support is more modest and more useful. Drinking water before meals fills the stomach and modestly reduces how much people eat. Staying well hydrated helps you tell thirst from hunger. And every glass of water that replaces a sugary drink removes calories without adding any. Our article on water and weight loss walks through the studies.
How this calculator works
It first runs the same math as our daily intake calculator — a weight-based baseline with adjustments for exercise, climate and life stage — because losing weight doesn't change your physiological need for water. Then it adds two extras: a pre-meal water amount of 500 ml, taken 30 minutes before your main meals, and a calorie-swap estimate based on how many sugary drinks you currently have each day.
The pre-meal trick, honestly
In the best-known trial, adults on a calorie-restricted diet who drank 500 ml of water before each meal lost about 2 kg more over 12 weeks than those who didn't. That is a real effect, but note the setting: everyone was already dieting. Water helped them eat a little less. It did nothing on its own. Our calculator shows how much of your daily target the pre-meal glasses cover, so you can see they're not extra volume, just better-timed volume.
The calorie swap is the bigger lever
For many people, sugary drinks are the largest single source of added sugar in their diet. One can of soda a day is around 50,000 kcal a year. Swapping it for water, sparkling water or unsweetened tea is the easiest calorie cut most people will ever make. If you find plain water boring, read our guide to swapping sugary drinks for water without feeling deprived.
