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		Phosphorus on label

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Show reference values

The following information is for guidance only and is not an assessment of any particular food. Whether a food is suitable for a specific cat cannot be derived from a single phosphorus value.

The nutritional guidelines of the European pet food industry federation FEDIAF recommend a minimum phosphorus content for complete foods for adult cats of 0.26 % of dry matter or 64 mg per 100 kcal of metabolisable energy. For indoor and neutered cats, for which FEDIAF assumes a lower energy requirement, the value is 0.35 % DM or 85 mg per 100 kcal; for growth and reproduction it is 0.84 % DM or 210 mg per 100 kcal FEDIAF 2025.
The FEDIAF values are a voluntary industry recommendation, not a legal limit. The dry-matter values assume an energy density of 4 kcal per gram of dry matter and need to be corrected for foods with a different energy density FEDIAF 2025. The per-100-kcal value does not need this correction.
For cats with kidney disease, IRIS names a phosphate-restricted renal diet as the first step to lower blood phosphate IRIS 2026.
The IRIS treatment recommendations are based on the blood phosphate value and the IRIS stage of the cat. They do not state a fixed phosphorus content for the food IRIS 2026.

Reference values as of September 2026. Sources below.

Why isn't the percentage on the can enough?

Cat foods contain different amounts of water. The label states how much under “moisture” – for wet food this value is naturally much higher than for dry food.

If phosphorus is simply given as a percentage of the whole food – that is, as fed (the food as it is in the can or pouch) – the water is included. Two foods can therefore show very different values on the label even though the phosphorus content of the actual nutrient mass is similar.

Dry matter is the food without its water. A value “on a dry matter basis” therefore describes the nutrient concentration regardless of how much water the product contains. This makes it easier to compare:

different wet foods with each other
wet food and dry food
foods with different water contents

Example

Food A

Water80 %
Phosphorus on label0.20 %
Dry matter20 %
Phosphorus DM1.00 %

0.20 ÷ 20 × 100 = 1.00 % DM

Food B

Water70 %
Phosphorus on label0.25 %
Dry matter30 %
Phosphorus DMapprox. 0.83 %

0.25 ÷ 30 × 100 ≈ 0.83 % DM

Although food B appears to contain more phosphorus at 0.25 % on the label, it contains less phosphorus than food A on a dry matter basis.

Enter the moisture for dry food, too

Dry food labels also state a moisture value. For an accurate calculation, use this value instead of assuming 0 %. Mathematically, the higher the dry matter content of a food, the smaller the difference between the label value and the dry matter value.

Why look at mg phosphorus per 100 kcal?

Dry matter allows a good comparison of nutrient concentration. It does not, however, take into account how energy-rich a food is – its energy density (calories per amount of food).

Mathematically, providing the same amount of energy takes more grams of a lower-energy food than of a higher-energy one – and therefore also more of the phosphorus it contains.

The figure mg phosphorus per 100 kcal shows how much phosphorus comes with 100 kcal from this food. This makes it easier to compare foods with different energy densities.

The FEDIAF nutritional guidelines also state their nutrient recommendations per 1,000 kcal. Their dry-matter values assume an energy density of 4 kcal per gram of dry matter and have to be corrected for other energy densities FEDIAF 2025.

Phosphorus and chronic kidney disease

Phosphorus is an essential nutrient for which the FEDIAF nutritional guidelines set minimum levels in food FEDIAF 2025.

For cats with chronic kidney disease (CKD), the International Renal Interest Society (IRIS) recommends reducing phosphate intake so that the blood phosphate value stays within a target range. According to IRIS, evidence suggests that this is beneficial for cats with kidney disease. The first step is a phosphate-restricted renal diet; if the value remains too high, phosphate binders are added IRIS 2026.

The target values depend on the IRIS stage. IRIS also names further laboratory values for the decision, such as FGF23, and recommends monitoring calcium: cats whose blood phosphate is already within the target range may be at increased risk of high calcium levels when renal diets are introduced IRIS 2026.

A calculator therefore cannot decide whether a particular food is medically suitable for an individual cat. This page deliberately does not classify foods as “good” or “bad” and does not use a traffic-light rating based on a single phosphorus value.

Phosphorus or phosphate?

The two terms sound similar but do not mean the same thing:

Phosphorus refers to the nutrient or chemical element as stated in the feed analysis (e.g. “phosphorus 0.17 %”).
Phosphate is the compound whose value is measured in the blood. The IRIS target values also refer to the blood phosphate value IRIS 2026.

The calculator on this page works exclusively with the phosphorus content of the food. It says nothing about a cat's blood phosphate level.

Method and formulas

All inputs are first converted to consistent internal base values:

Phosphorus in mg per 100 g of food, as it is in the package
Moisture in %
Energy in kcal per 100 g

Phosphorus units

% (as on the label) → mg/100 g = value × 1000
mg/100 g → used as is
mg/kg → mg/100 g = value ÷ 10
g/kg → mg/100 g = value × 100
% of dry matter → % as on the label = value × dry matter ÷ 100

Energy units

kcal/100 g → used as is
kcal/kg → kcal/100 g = value ÷ 10
MJ/kg → kcal/kg = value × 239.006, then ÷ 10

Estimating energy (if not stated)

If the energy content is missing, it can be estimated from the analytical constituents. The calculator uses the prediction equation for cats from the FEDIAF nutritional guidelines (based on NRC 2006) FEDIAF 2025. All values in %, as on the label:

NFE (%) = 100 − moisture − crude protein − crude fat − crude ash − crude fibre
Gross energy = 5.7 × crude protein + 9.4 × crude fat + 4.1 × (NFE + crude fibre)
Digestibility (%) = 87.9 − 0.88 × crude fibre in dry matter
Metabolisable energy (kcal/100 g) = gross energy × digestibility ÷ 100 − 0.77 × crude protein

NFE stands for “nitrogen-free extract”, essentially the carbohydrates. It is not stated on the label and is therefore calculated as the remainder. If the declared values add up to slightly more than 100 % due to rounding, NFE is set to 0. An energy value from the manufacturer always takes precedence over the estimate.

Key figures

Dry matter (%) = 100 − moisture (%)
Phosphorus DM (%) = phosphorus (g/100 g) ÷ dry matter (%) × 100
Phosphorus (mg/100 kcal) = phosphorus (mg/100 g) ÷ energy (kcal/100 g) × 100
Phosphorus (mg/1,000 kcal) = phosphorus (mg/100 kcal) × 10
Daily intake (mg) = phosphorus (mg/100 g) × amount of food (g/day) ÷ 100

Calculations use full precision internally; values are only rounded for display (dry matter to two decimal places, mg per 100 or 1,000 kcal to whole numbers). If phosphorus was already entered as % of dry matter, it is not converted again using the moisture.

Plausibility notes

A note appears below a field if a value is probably due to a typing or unit error – for example, if an energy content would mean more energy per gram of dry matter than pure fat provides (9.4 kcal gross energy per gram FEDIAF 2025). Such notes do not assess any food and do not prevent a calculation.

Numbers with a comma followed by exactly three digits, e.g. “1,700”, are read as thousands. The note below the field then shows how the value was understood.

Frequently asked questions

How do I convert phosphorus to a dry matter basis?

First subtract the moisture from 100 – this gives the dry matter share. Then divide the phosphorus value from the label by this share and multiply by 100.

Example: 0.17 % phosphorus at 80 % moisture gives 20 % dry matter and therefore 0.17 ÷ 20 × 100 = 0.85 % phosphorus in the dry matter. This is a plain unit conversion; the calculator above does it automatically.

Why also mg phosphorus per 100 kcal?

This value relates phosphorus to the energy the food provides. The FEDIAF nutritional guidelines also state their nutrient recommendations per 1,000 kcal FEDIAF 2025.

The FEDIAF dry-matter values assume an energy density of 4 kcal per gram of dry matter. If a food differs, they have to be corrected according to FEDIAF FEDIAF 2025. The per-100-kcal value does not need this correction.

What is the minimum phosphorus content of cat food?

The FEDIAF nutritional guidelines state these minimum levels for complete foods (DM = dry matter) FEDIAF 2025:

Cat	% DM	mg/100 kcal
adult	0.26	64
adult, indoor or neutered	0.35	85
growth and reproduction	0.84	210

These are minimum values for healthy cats from a voluntary industry guideline – not legal limits and not recommendations for cats with a disease.

How much phosphorus should food for cats with kidney disease contain?

The International Renal Interest Society (IRIS) does not state a fixed phosphorus content for the food. Its treatment recommendations are based on the blood phosphate value IRIS 2026.

According to IRIS (2026), evidence suggests that cats with chronic kidney disease benefit from a long-term reduction of phosphate intake that keeps blood phosphate below 1.5 mmol/l (4.5 mg/dl), but not below 0.9 mmol/l (2.7 mg/dl). As a more realistic target under treatment, IRIS names below 1.6 mmol/l (5.0 mg/dl) for stage 3 and below 1.9 mmol/l (6.0 mg/dl) for stage 4 IRIS 2026.

According to IRIS, the first step is a phosphate-restricted renal diet. If the value remains above target, phosphate binders are added. Which measure is right is decided by the veterinary practice based on the laboratory values IRIS 2026.

Is less phosphorus always better?

No, not across the board. Phosphorus is an essential nutrient for which FEDIAF sets minimum levels FEDIAF 2025. Even for cats with kidney disease, IRIS names a lower limit for blood phosphate (0.9 mmol/l) IRIS 2026.

IRIS also points out that cats whose blood phosphate is already within the target range may be at increased risk of high calcium levels when renal diets are introduced IRIS 2026. This calculator therefore deliberately does not rate foods.

Does it matter where the phosphorus in the food comes from?

According to FEDIAF, high intakes of highly bioavailable inorganic phosphorus compounds (e.g. sodium dihydrogen phosphate) of 1.5 g per 1,000 kcal or more can affect indicators of kidney function in cats. Studies with 1 g per 1,000 kcal showed no detectable adverse effects on renal health in healthy adult cats. FEDIAF considers further research necessary FEDIAF 2025.

The calculator works with the total phosphorus stated. It cannot tell which sources the phosphorus comes from.

How accurate is the energy estimate?

The calculator uses the prediction equation from the FEDIAF nutritional guidelines (based on NRC 2006). According to FEDIAF, it estimates the energy content of dry food more accurately than the so-called modified Atwater factors; for wet food, both methods are only moderately accurate FEDIAF 2025. If an energy content is stated on the package, it should be preferred – the calculator then uses it automatically.

Are my inputs stored or transmitted?

No. All calculations run in your browser. Data is only stored when you click “Save food” – and only on your device. A backup is downloaded as a file to your own device. When you share a link, the values are contained in the link itself and are only read in the recipient's browser when it is opened.

Sources & date

Medical information and reference values as of September 2026.

Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs. FEDIAF (European Pet Food Industry Federation), September 2025 edition. europeanpetfood.org – Nutritional Guidelines. Accessed 16 September 2026. Used for: minimum phosphorus levels (tables III-4a/b), conversion assuming 4 kcal per gram of dry matter (table III-2), inorganic phosphorus compounds (footnote f), energy estimate and gross energy of nutrients (chapter 7.2.2), energy requirement of indoor and neutered cats (chapter 7.2.4.2).
Treatment Recommendations for CKD in Cats. International Renal Interest Society (IRIS), modified 2026. iris-kidney.com – IRIS Guidelines. Accessed 16 September 2026. Used for: blood phosphate targets by stage, stepwise approach (renal diet, phosphate binders), FGF23 and calcium monitoring.

The conversion formulas are plain unit calculations and need no source. Medical and nutritional statements on this page are marked with their source where they appear.

Please note

This calculator is intended solely for information and for comparing foods. It cannot replace a veterinary diagnosis, nutritional advice or treatment recommendation.

In chronic kidney disease, the choice of food, laboratory values, phosphate target and, if applicable, the use of phosphate binders should be agreed with the treating veterinary practice.

Phosphorus Calculator for Cat Food