Weight loss calculator: how long will reaching your goal take?

The number of weeks is simple arithmetic: kilograms to lose divided by the pace you picked. Treat it as a horizon, not a deadline. Every longer stretch of fat loss has weeks where the scale holds still and weeks where it drops 1.5 kg at once. The monthly average tells you more than any single week.

The calorie deficit comes from the standard conversion: 1 kg of body weight is roughly 7,700 kcal. To lose 0.5 kg a week you need about 550 kcal of deficit a day. It does not all have to come from food. Part of it can come from movement, and that part is usually the easiest to sustain.

The first weeks lie. At the start the scale can drop 2-3 kg in a few days. That is water bound to glycogen and less food in your gut, not fat. The same works in reverse: when you stop, some of it comes back, and that is not fat either.

Body weight is not the whole story. If you lift, you can lose fat and build a little muscle at the same time, so the scale slows down while your shape keeps changing. That is why I track measurements and photos alongside weight with my clients.

• Kilograms to lose = current weight minus target weight.
• Time [weeks] = kilograms to lose ÷ chosen pace [kg/week], rounded up to a whole week.
• Daily deficit = pace [kg/week] × 7,700 kcal ÷ 7. The 7,700 kcal per kilogram figure is the standard approximation for fat tissue.
• Available paces: 0.25 kg/week, 0.50 kg/week, 0.75 kg/week. Any pace above 1 percent of body weight per week is flagged as too aggressive.
• The chart is a linear projection. A real weight curve is never a straight line, but a linear illustration shows the scale of time well.

Someone weighing 80 kg wants to get to 72 kg, so they have 8 kg to lose.

• 0.25 kg/week → roughly 32 weeks, a deficit of about 275 kcal a day
• 0.50 kg/week → roughly 16 weeks, a deficit of about 550 kcal a day
• 0.75 kg/week → roughly 11 weeks, a deficit of about 825 kcal a day

Realistically I would plan for 16 to 32 weeks here, leaving room for holidays and for the weeks when the scale refuses to move.

• Picking the fastest pace to “save time”. A stretch of fat loss you abandon halfway takes forever. The one you finish takes exactly as long as the calculator says.
• A target weight plucked from thin air. “I want to weigh what I did at school” is rarely a sensible goal twenty years later. Measurements, how you feel and how your clothes fit are better reference points.
• No plan for afterwards. The hard part is not the deficit, it is going back to eating at maintenance without rebounding. That stage is worth planning in advance.
• Dieting without strength training. Then you lose both fat and muscle, and when it is over your energy needs are lower than they should be.
• Weighing daily and drawing conclusions daily. Weigh yourself every day if you like, but draw your conclusions from the weekly average.

If you live in Kraków and want to go through fat loss with a trainer, I run personal training at a small private studio at Zawiła 61A, where Ruczaj meets Kliny. I work mostly with beginners, with people returning to activity and with people who want to lose weight and stop starting over every six months.

Have a look at 1:1 personal training or online coaching if you live further away.