The zig zag diet calculator, step by step
This calculator turns three inputs, your weight, height, and age, into a resting metabolic rate, scales it by activity, applies a deficit you choose, then splits the result into high and low days around a fixed weekly average. Everything follows standard equations, so you can check the arithmetic by hand afterwards.
The worked example
| Step | Arithmetic | Result |
|---|---|---|
| 1. Resting rate (Mifflin-St Jeor, F4) | 10 × 70 kg + 6.25 × 165 cm − 5 × 35 y − 161 | 1395 kcal/day |
| 2. Active rate (moderate ×1.55, F9) | 1395 × 1.55 | 2162 kcal/day |
| 3. Deficit target (−500, F5) | 2162 − 500 | 1662 kcal/day |
| 4. Low days (80% of target) | 1662 × 0.8 | 1330 kcal ×4 days |
| 5. High days (balance the week) | (7 × 1662 − 4 × 1330) ÷ 3 | 2105 kcal ×3 days |
Activity multipliers
| Activity | What it means | Multiplier |
|---|---|---|
| Sedentary | desk work, no training | ×1.2 |
| Light | walks or training 1–3 days a week | ×1.375 |
| Moderate | training 3–5 days a week | ×1.55 |
| High | hard training 6–7 days a week | ×1.725 |
From BMR to TDEE
Start with the Mifflin-St Jeor equation from 1990: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age(y) + 5 for men and - 161 for women. Multiply that resting number by an activity factor, sedentary x1.2, light x1.375, moderate x1.55, high x1.725, to get your total daily energy expenditure.
The activity factor is the only judgement call here. Pick the honest one: a desk job with a couple of walks is sedentary or light, not moderate. Overstating it inflates every number downstream, including the high and low days you set at the end.
Choosing the deficit
One kilogram of body fat stores about 7700 kcal, so an average deficit of 500 kcal per day gives about 0.45 kg of loss per week. That sits inside the commonly cited safe rate of 1-2 lb (0.45-0.9 kg) per week, which is where most people should aim.
The equation cannot see medical history. If you live with a persistent condition, take prescription medication, or have a history of disordered eating, that belongs with a physician rather than a spreadsheet: bring your numbers to the appointment instead of adjusting around them.
Setting the high-low split
Take your deficit target as the weekly average, then swing the days: a typical zigzag keeps high days at +15-25% and low days at -15-25% around that daily number, and the week still totals what a steady diet would. Match high days to training days so the extra energy has somewhere to go.
Keep the swing modest at first. The widest swing ever studied runs from 25% of energy needs on low days to 125% on high days, and most people find a gentler pattern easier to hold week after week than a trial-scale swing.