Standard calorie calculators ask you to pick one activity level for the entire week. If you work a rotating or 12-hour shift schedule, that single number is quietly wrong on both kinds of day. This tool starts from the same biology every other calculator uses, then treats your week the way it actually happens: as two different kinds of day, not one average day repeated seven times.

It starts with your baseline. Age, sex, height, and weight go into the Mifflin-St Jeor equation, the same formula used across the fitness industry, to get your BMR: the energy your body burns at complete rest, before any activity is added.

Next comes your week, built one day at a time. If your job matches one of the four presets, picking it fills in a typical shift multiplier and a typical week pattern for you, both fully editable afterward. Below that sits a seven-tile grid, one tile per day. Click a tile to flip it between a shift day and an off day. Because the grid always has exactly seven tiles, there is no separate count of work days and rest days to keep in sync; the split is the grid itself.

Each day type gets its own activity level, chosen from the same five standard levels every TDEE calculator uses, from sedentary to extra active. Shift days and off days are allowed to sit at different levels, because they usually are different.

Right under that is a third question most calculators never ask: which single level you would have picked if you were only allowed to enter one. This is what makes the comparison honest. Instead of inventing an average of your two levels, the tool asks you directly, then compares your true week against your own answer.

The results panel shows three numbers side by side, not one: your target for a shift day, your target for an off day, and your true weekly average, blended across however many of each you actually have. Underneath, a balance bar shows what share of your week’s total energy comes from shift days versus off days. Next to it, three small stats surface your highest day, your lowest day, and your average, each one labeled by which kind of day it is.

Below the numbers is the weekly wave: seven columns, one per day, each as tall as that day’s real calorie need. A dotted line cuts across the chart at the level you said you would have picked on a standard calculator. Where your columns rise above or dip below that line is exactly where a flat number would have gotten it wrong. Hover any column for its exact figure.

Underneath the wave sits a smaller gauge. Its needle leans toward under or over depending on whether a flat number would have underfed or overfed you across the week, and the exact weekly gap is printed above it in kcal.

Two actions sit below the results. Add a shift flips your next off day into a shift day and recalculates everything instantly, a quick way to see what picking up extra work would do to your numbers. Reset to defaults clears everything back to a plain starting point.

Show the math expands the full calculation with your own numbers filled in: the BMR formula, both activity multipliers, the weekly total, the true average, and the gap against the level you said you would have chosen. Nothing is hidden and nothing is estimated on your behalf.

This is a starting estimate, not a medical recommendation. Mifflin-St Jeor predicts resting energy needs within about ten percent for most people; use your real weight trend over two to three weeks to fine-tune from here.