Calculator inputs
Example data table
| Profile | TDEE | Fast day kcal | Feed day kcal | Goal |
|---|---|---|---|---|
| Female, 34, 72 kg, moderate | 2,167 | 542 | 1,823 | Weight loss |
| Male, 41, 86 kg, active | 2,963 | 741 | 2,301 | Weight loss |
| Female, 29, 61 kg, light | 1,882 | 471 | 1,647 | Mild loss |
Formula used
BMR: The calculator uses Mifflin-St Jeor when body fat is unknown. If body fat is entered, it can use Katch-McArdle.
TDEE: Total daily energy expenditure equals BMR multiplied by an activity factor.
Weekly target: Weekly target calories = (TDEE × 7) − weekly deficit chosen by goal.
Fast days: Fast day calories either equal a chosen percentage of TDEE or a custom calorie value.
Feed days: Feed day calories = (weekly target calories − total fast day calories) ÷ 5.
Predicted change: Estimated weekly body change uses 7,700 kcal per kilogram and 3,500 kcal per pound as planning conversions.
How to use this calculator
- Enter age, sex, body size, and activity level.
- Select metric or imperial units and fill the correct fields.
- Choose your goal such as maintenance, mild loss, or stronger loss.
- Pick a fasting day method using a TDEE percentage or custom calories.
- Leave feeding days on auto for balanced planning, or set custom calories.
- Submit the form and review the result panel above the form.
- Export the visible results as CSV or PDF when needed.
- Use the result as a planning guide, not as medical advice.
8 FAQs
1. What is a 5:2 diet?
It is an eating pattern with five normal intake days and two lower calorie days each week. The goal is weekly calorie control without fasting every day.
2. How are fasting calories chosen?
Many people use around 20% to 30% of maintenance calories on fasting days. This calculator also lets you enter a custom calorie target.
3. Why do feeding day calories matter?
Feeding days determine whether your full week matches maintenance, fat loss, or surplus goals. High feeding days can erase the weekly fasting deficit.
4. Is the weekly weight change exact?
No. It is a planning estimate based on calorie balance. Real changes vary with water retention, adherence, hormonal factors, and measurement error.
5. Should I use body fat percentage?
Use it only if you have a reasonably accurate estimate. When supplied, the calculator can apply the Katch-McArdle method for BMR estimation.
6. Can I choose any two fasting days?
Yes, many people separate them for comfort and consistency. Choose days that fit training, work, and family routines best.
7. Is this plan suitable for everyone?
Not always. People with medical conditions, pregnancy, eating disorder history, or medication needs should speak with a qualified clinician first.
8. What if my feeding day calories look too low?
That can happen with aggressive targets or very low fasting calories. Try a milder goal, higher fasting intake, or discuss a safer plan professionally.