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ANSWER

How many calories should I eat with a Garmin or WHOOP?

Updated October 28, 2026

Short answer

Start from your watch's average total daily burn (active plus resting calories) over the last 3–7 complete days, not today's running total and not a single day. That average is your estimated maintenance: eat about that to keep your weight, about 15% less to lose fat, or a little more (Plait uses 8%) to gain muscle. Then watch your weight trend for 2–3 weeks and adjust, because watch calorie figures are estimates.

Worked example

A 75 kg runner's last five complete Garmin days:

2,980 · 2,410 · 2,650 · 2,520 · 2,700 kcal

Average: 2,652 kcal a day. That is the estimated maintenance.

Plait's own target rule for this example (services/nutritionTargets.js).
GoalCaloriesProteinCarbohydrateFat
Maintain2,652 kcal135 g362 g74 g
Lose fat (15% below)2,254 kcal165 g257 g63 g
Gain muscle (8% above)2,864 kcal143 g393 g80 g

Step by step

  1. Use total daily burn, not active calories alone. On Garmin that is active plus resting calories; on WHOOP it is the day's calories for the whole cycle.
  2. Only count finished days. Today's number keeps growing until midnight (or until you wake, on WHOOP).
  3. Average at least 3 recent complete days, ideally a full week, so one race or one rest day does not set your whole plan.
  4. Adjust for your goal: about 15% below maintenance to lose fat, a small surplus to gain muscle. Do not go below a safe floor (Plait never plans under 1,200 kcal a day).
  5. Set protein first, about 1.4–2.0 g per kg of body weight for people who train, then split the rest between carbohydrate and fat.
  6. Check the trend. If your weight moves faster or slower than you expect over 2–3 weeks, change the target by 100–200 kcal a day rather than trusting any single number.

Why the number changes from day to day

Your burn is not the same every day. In Plait's October 2026 data kit, the median Garmin user's highest-burn day was 712 kcal above their lowest day in the same week (124 users). A fixed daily target eats the same on a long run day and on a rest day.

Plait uses the weekly average for your plan. With Plait Pro, today's portions also adjust each morning to yesterday's training: today's carbohydrate and fat change by 60% of the difference between yesterday's measured burn and the burn your plan is built for. Differences under 150 kcal are ignored, a day changes by at most 800 kcal, and protein stays the same. Free accounts keep the weekly plan and see what Pro would change on big days.

How far to trust the watch

Wrist devices estimate energy expenditure; they do not measure it. Independent studies find large errors for single sessions, and in Plait's data Garmin's resting estimate ran a median 22% above the Mifflin–St Jeor formula across 78 Garmin users. An average over several days is steadier than any single day, and your weight trend is the final check.

Questions

Should I eat back my Garmin active calories?

Not on top of a target that already includes them. If your target comes from your average total burn (active plus resting), your training is already in it. Eating back every active calorie on top of that counts the same exercise twice.

Is the WHOOP calorie number accurate enough to plan meals?

It is an estimate, like every wrist device. It is useful as a multi-day average for setting maintenance, then your weight trend over 2–3 weeks tells you whether to move the target up or down.

How many days of watch data do I need?

At least 3 complete days; a full week is better because it includes both hard and easy days. Until then, a formula such as Mifflin–St Jeor times an activity factor is a reasonable starting estimate.

Does Plait change my calories every day?

Plait sets your target from the average of recent complete days. With Pro, today's carbohydrate and fat portions also adjust each morning to yesterday's measured burn; protein stays the same and the weekly plan and shopping list do not change.

Sources

  1. Thomas DT, Erdman KA, Burke LM. Nutrition and Athletic Performance (ACSM, Academy of Nutrition and Dietetics, Dietitians of Canada joint position). Med Sci Sports Exerc 2016;48(3):543–568. pubmed.ncbi.nlm.nih.gov
  2. Jäger R et al. ISSN position stand: protein and exercise. J Int Soc Sports Nutr 2017;14:20. pubmed.ncbi.nlm.nih.gov
  3. Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51(2):241–247. pubmed.ncbi.nlm.nih.gov
  4. Plait wearable data kit, October 2026 (aggregates of at least 30 users). www.plait.fit

Wearable calorie figures are estimates. Nutrition guidance here is general information, not medical care.