Swimming for Weight Loss: How Often, How Hard and Calories Burned

Swimming can be a good part of losing weight. It is not a shortcut, and nobody can promise you a number of kilos in a number of weeks. What it can be is a form of exercise you are able to keep doing, week after week, which is the part that matters most. This guide covers what swimming can and cannot do, how many calories it uses according to the reference tables researchers use, and how to organise your week.

What swimming can and cannot do

Your weight depends on the balance between the energy you take in with food and the energy you use. Exercise is one side of that balance; what you eat is the other.

The US Centers for Disease Control and Prevention (CDC) put it plainly: most weight loss comes from eating fewer calories, while regular physical activity is what helps you keep the weight off. Reaching and staying at a healthy weight takes both.

So swimming works best as one half of a plan, with food as the other half. If you want to lose a significant amount of weight, a doctor or a registered dietitian can help you set a plan that is right for you.

How many calories does swimming burn?

Researchers estimate the energy cost of activities with the Compendium of Physical Activities, a reference list of activities and their MET values. A MET says how many times more energy an activity uses than sitting quietly at rest. A value of 6 means about six times the resting rate.

These are the MET values for swimming in the 2024 Adult Compendium:

• Freestyle laps, slow, recreational: 5.8
• Freestyle laps, fast, vigorous effort: 9.8
• Breaststroke, recreational: 5.3
• Backstroke, recreational: 4.8
• Butterfly, general: 13.8
• Leisurely swimming, not laps: 6.0

From METs to calories

One MET is roughly 1 kcal per kilo of body weight per hour. So a rough estimate is:

calories (kcal) = MET x your weight in kg x hours

A worked example for a person who weighs 70 kg:

• 30 minutes of slow, recreational freestyle laps: 5.8 x 70 x 0.5 = about 200 kcal
• 30 minutes of fast, vigorous freestyle: 9.8 x 70 x 0.5 = about 340 kcal

Read these numbers with care:

• They are averages. The Compendium's authors say the values are a starting point and do not reflect precise individual energy use. Age, sex, height, body weight and body composition all change the real figure.
• They include what you would burn anyway. Sitting still for the same half hour would use about 35 kcal (1 x 70 x 0.5). The extra cost of swimming is the difference.
• Time in the pool is not time swimming. If you spend 10 of your 30 minutes resting at the wall, you swam for 20.

If you want a number to track, track your sessions and your distance. Those you can control.

How often and how long to swim

WHO advises adults at least 150 minutes a week of moderate activity for health, and the CDC gives the same figure. Three sessions of 50 minutes reach it.

If you are starting from little or no exercise, begin with two sessions a week of 30 to 45 minutes, rests included, and add the third session when two feel comfortable. If you cannot yet swim a few lengths without stopping, the beginner swim workout plan builds up from 25 m repeats.

Fixed days help more than good intentions. Pick the days and times you can actually keep, and treat them like an appointment.

Mix steady swimming and harder sets

Not every session needs to leave you exhausted. A week works better with two kinds of work.

Steady swimming. Longer swims or long repeats at a pace where you could say a short sentence at the wall. It builds your base, it is easy to recover from, and you can do a lot of it.

Harder sets. Shorter repeats at a faster pace, with rest in between, for example 8 x 50 m a little faster than usual with 30 seconds of rest. In the Compendium, fast freestyle has a higher MET value than slow freestyle, so the minutes you spend swimming harder cost more energy. They are also harder to sustain, which is why they come in short pieces with rest.

Keep most of the week steady and add one or two harder blocks. If every session is hard, you are more likely to end up tired and skip the next one.

Two example sessions in a 25 m pool (indicative, adjust to your level):

Session A, steady (1500 m)

• 200 easy
• 4 x 50 kick with a board, 20 s rest
• 3 x 300 freestyle at a steady pace, 30 s rest
• 200 easy

Session B, mixed (1300 m)

• 300 easy, mixed strokes
• 8 x 50 freestyle a little faster, 30 s rest
• 4 x 100 steady, any stroke, 20 s rest
• 200 easy

If the notation is new to you, see how to read a swim workout.

Why swimming suits many people with sore joints

In water, part of your body weight is supported, and there is no landing like there is in running or jumping. That is why many people with sore knees, hips or back find swimming more comfortable than other sports.

This is not a treatment. If you have joint pain, a condition, or you are coming back from an injury, ask your doctor or physiotherapist which strokes and how much swimming suit you. If a stroke hurts, stop and change stroke.

Consistency beats everything else

• Keep a log. Date, distance, main set, how it felt. Progress in the water, like more lengths without stopping or a faster 400 m, is something you can see every few weeks.
• Do not judge one week. Body weight goes up and down from day to day. Look at the trend over weeks, and at your swimming, not at a single morning.
• Plan your meals around swimming. Some people notice they are hungry after a swim. Deciding in advance what you will eat afterwards makes it easier to stick to your plan.
• Vary the sessions. The same session every time gets boring and stops moving you forward. Our article on why lap swimming plateaus explains what to change.

Talk to your doctor first if

You have a heart condition, high blood pressure, diabetes or another health condition, you are pregnant, you have not exercised for a long time, or you want to lose a lot of weight. Your doctor can tell you how to start safely.

A plan you can keep

SwimSensei builds a plan from your level, the days you train and your pool length (25, 33 or 50 m), and adapts it every week to what you actually swam. See how it works on the swimmers page and ask for early access.