How to Calculate Carbohydrates in Pet Food
Most dog and cat food labels don’t list carbohydrate directly. Instead, it’s commonly estimated by difference: subtract moisture, crude protein, crude fat, crude fiber, and ash from 100%. This calculated value is often called nitrogen-free extract (NFE).
The result is an estimate, not a laboratory-measured carbohydrate value — and it can be shown either as-fed (as the food sits in the bag or can) or converted to a dry-matter basis for a moisture-adjusted comparison.
Want the math done for you? Use the free Pet Food Carbohydrate Calculator to get an as-fed and dry-matter estimate from your label values.
Use the Carb Calculator →Why Isn’t Carbohydrate Listed on Many Pet Food Labels?
In the United States, AAFCO’s Guaranteed Analysis requirements cover four core values: a minimum percentage of crude protein, a minimum percentage of crude fat, a maximum percentage of crude fiber, and a maximum percentage of moisture. Carbohydrate is not one of the required guarantees, so most labels simply don’t show it. Ash is not a standard requirement either — if a manufacturer chooses to list it, it appears as a maximum, placed after moisture.
Because carbohydrate isn’t required, pet owners who want a sense of a food’s carbohydrate content generally have to calculate an estimate themselves from the values that are available.
What Is Carbohydrate by Difference?
Carbohydrate by difference is a standard approach used in pet food (and animal feed generally): measure moisture, crude protein, crude fat, crude fiber, and ash, then treat whatever percentage is left out of 100% as the carbohydrate fraction. It’s a subtraction, not a direct chemical test for carbohydrate molecules.
What Is Nitrogen-Free Extract (NFE)?
The technical name for this calculated remainder is nitrogen-free extract, or NFE. The name reflects how it’s produced: everything containing nitrogen (mainly protein) has already been subtracted, along with fat, fiber, moisture, and ash, so what’s left is described as “free” of those components.
NFE is a useful estimate, but it isn’t a pure carbohydrate measurement. It can also capture soluble fiber that isn’t caught by the crude fiber test, along with vitamins and small amounts of testing error — so it can run a little higher than the food’s true digestible carbohydrate content, particularly in foods with a lot of soluble fiber.
Pet Food Carbohydrate Formula
Estimated carbohydrate/NFE (% as-fed):
100 − moisture % − crude protein % − crude fat % − crude fiber % − ash %
Each value comes from the food’s Guaranteed Analysis or, for ash, from the manufacturer’s fuller nutrient information (more on that below). The result is the estimated carbohydrate/NFE percentage as the food is sold — including its water content.
Step-by-Step Example
Say a label shows: Moisture 10%, Crude Protein 25%, Crude Fat 15%, Crude Fiber 4%, and the manufacturer’s nutrient sheet lists Ash at 8%.
Add up everything except carbohydrate:
10 + 25 + 15 + 4 + 8 = 62%
Subtract from 100%:
100 − 62 = 38%
Estimated carbohydrate/NFE (as-fed) ≈ 38%.
These numbers are illustrative only and don’t represent a specific real product. Enter your own label’s values into the Carb Calculator to get a real estimate.
Why Ash Matters
Ash is the inorganic, mineral portion of the food — what’s left after everything else is burned off in a lab test. It isn’t a measure of food quality by itself, and a higher or lower ash number doesn’t automatically make a food better or worse. It matters here purely because of the math: the by-difference formula subtracts five specific values from 100%, and ash is one of them. Leave it out, and the “carbohydrate” figure would actually include the food’s mineral content too, overstating the estimate.
What If Ash Isn’t Listed?
Ash usually isn’t part of the standard Guaranteed Analysis panel, so you may need to look further than the front or back of the bag. A few practical options:
- Check the manufacturer’s full nutrient analysis or “typical analysis,” often published on their website or available as a technical/product data sheet.
- Contact the manufacturer directly and ask for the ash (sometimes labeled “crude ash”) percentage for that specific product.
PawCalcHub’s Carb Calculator requires a real ash value and does not substitute an assumed number — there isn’t a well-supported industry-standard default, and guessing would make the estimate less reliable, not more.
As-Fed vs Dry-Matter Carbohydrate
As-fed is the percentage as the food actually sits in the bag or can, water included. Dry-matter basis mathematically removes that water, so you’re comparing only the solid, dry portion of the food.
This distinction matters because moisture content varies enormously between products — canned/wet foods are often 70–80% water, while dry kibble is typically under 12%. Comparing two foods’ as-fed numbers side by side can be misleading when their moisture levels are that different; converting to dry-matter basis puts them on more comparable footing. It doesn’t, on its own, tell you which food is healthier or better suited to a particular pet — it just removes water from the comparison.
For a full walkthrough of dry-matter conversions and comparisons, see the Dry Matter Basis in Pet Food guide. To convert an individual nutrient value yourself, the Dry Matter Calculator handles that conversion directly.
Example: Why Moisture Changes the Comparison
A wet-food-style label: Moisture 78%, Crude Protein 10%, Crude Fat 5%, Crude Fiber 1%, Ash 2%.
100 − 78 − 10 − 5 − 1 − 2 = 4% estimated carbohydrate/NFE as-fed.
Dry matter is 100 − 78 = 22%. On a dry-matter basis, that same 4% becomes 4 ÷ 22 × 100 ≈ 18.2%.
As-fed, this food looks very low in carbohydrate — but once water is factored out, the dry-matter estimate is meaningfully higher. This is why as-fed numbers alone can be misleading when comparing a wet food to a dry food. These figures are hypothetical and don’t represent every wet food.
Limitations of Guaranteed Analysis
Guaranteed Analysis values aren’t exact measured composition figures. By labeling convention, crude protein and crude fat are listed as minimums, while crude fiber and moisture are listed as maximums — meaning the actual nutrient content of the food can differ from the guaranteed numbers, usually in the food’s favor for protein and fat. A carbohydrate/NFE estimate built from these values inherits that same limitation: it’s only as precise as the guarantees it’s calculated from, not a laboratory-measured composition of the specific bag or can in front of you.
Can You Use Carb Percentage to Judge Pet Food Quality?
Not on its own. Carbohydrate/NFE percentage is one data point among many, and it doesn’t function as a quality score. A higher or lower estimated carbohydrate percentage doesn’t by itself make a food better, worse, premium, or poor quality, and it isn’t evidence that a food is or isn’t appropriate for a specific pet. Overall suitability depends on far more than one nutrient estimate — including the pet’s species, life stage, health status, and a veterinarian’s guidance.
When This Calculation Is Useful
This kind of estimate is useful for getting a general sense of a food’s carbohydrate/NFE content from its label, or for roughly comparing two foods you’re considering — on an as-fed basis, or on a dry-matter basis when their moisture levels differ a lot.
When to Ask Your Veterinarian
This calculation is not a diagnosis, a therapeutic diet recommendation, or a substitute for professional guidance. If you’re managing a specific health condition — diabetes, kidney disease, obesity, urinary or gastrointestinal issues, or anything else — carbohydrate targets and diet changes should be discussed with your veterinarian or a veterinary nutrition professional, who can consider your individual pet’s full history and needs.
Frequently Asked Questions
How do I calculate carbohydrates in pet food?
Subtract the label’s moisture, crude protein, crude fat, crude fiber, and ash percentages from 100%. The result is an estimated carbohydrate/NFE percentage on an as-fed basis. You can do this manually or use the Carb Calculator.
Why aren’t carbohydrates listed on pet food labels?
AAFCO’s Guaranteed Analysis requirements only cover minimum crude protein, minimum crude fat, maximum crude fiber, and maximum moisture. Carbohydrate isn’t part of that required list, so most labels don’t show it directly.
What does NFE mean in pet food?
NFE stands for nitrogen-free extract — the technical name for the carbohydrate-by-difference estimate. It’s what’s left after subtracting moisture, protein, fat, fiber, and ash from 100%, and it can include some soluble fiber and vitamins along with true carbohydrate.
Do I need the ash percentage to calculate carbohydrates?
Yes. Ash is one of the five values the formula subtracts from 100%, and there’s no well-supported standard default to substitute if it’s missing, so a real ash value is needed for a defensible estimate.
What if ash isn’t listed?
Check the manufacturer’s full nutrient analysis or technical/product data sheet, often available on their website, or contact the manufacturer directly and ask for the ash (or “crude ash”) percentage.
What is the difference between as-fed and dry-matter carbohydrates?
As-fed includes the water in the food as sold. Dry-matter basis mathematically removes that water, which makes it easier to compare foods with very different moisture levels, like canned and dry food.
Can I compare wet and dry pet food using as-fed carbohydrate?
It can be misleading. Wet foods are often 70–80% water, which dilutes every as-fed percentage. Converting both foods to a dry-matter basis gives a fairer comparison.
Does a higher carbohydrate percentage mean a food is unhealthy?
No. This estimate doesn’t function as a food-quality score, and carbohydrate percentage alone doesn’t determine whether a food is appropriate for a particular pet. Suitability depends on many factors, including your veterinarian’s guidance.
Sources: carbohydrate-by-difference / nitrogen-free extract (NFE) methodology and its limitations as described by Tufts University Cummings School of Veterinary Medicine (petfoodology), consistent with AAFCO Guaranteed Analysis labeling requirements. Citing these organizations is for sourcing purposes only and does not imply their endorsement of PawCalcHub. See our Methodology and Sources & References pages for how we research and cite our calculators generally.