Short answer: Dicalcium phosphate (CaHPO4, also known as DCP or calcium hydrogen phosphate) is a combined calcium-phosphorus mineral premix used in pet food to meet AAFCO 2024 canine and feline mineral minima. The anhydrous form supplies approximately 28–30 percent elemental calcium and 20–22 percent elemental phosphorus; the more common dihydrate form (CaHPO4·2H2O) supplies approximately 22–24 percent calcium and 17–18 percent phosphorus per AAFCO 2024 and FDA-CVM mineral ingredient specifications. Per AAFCO 2024 canine maintenance nutrient profile, dietary calcium minimum is 0.5 percent and maximum is 2.5 percent on a dry-matter basis; phosphorus minimum is 0.4 percent and maximum is 1.6 percent. Per NRC 2006 Nutrient Requirements of Dogs and Cats and AAFCO 2024, the calcium-to-phosphorus ratio target is 1:1 to 2:1, with the upper bound particularly relevant for large-breed puppy formulations per AAFCO 2020 Large Breed Puppy provisions. Dicalcium phosphate is the most common combined Ca+P mineral source in pet food because it efficiently delivers both minerals in approximately the target ratio without requiring separate calcium carbonate and phosphate salt additions. Per Heaney 1989 (J Bone Miner Res) mineral bioavailability framework, DCP calcium bioavailability is comparable to calcium carbonate and substantially less than calcium citrate. The KibbleIQ rubric treats DCP as a neutral mineral premix signal — expected presence in essentially every AAFCO-complete formulation.

Chemical identity and forms

Per AAFCO 2024 Official Publication ingredient definition and standard mineral chemistry references, dicalcium phosphate is the salt of dibasic phosphate (HPO42-) with calcium (Ca2+), molecular formula CaHPO4. Two crystalline forms appear in commercial supply: the anhydrous form (CaHPO4, also called monetite), and the more common dihydrate form (CaHPO4·2H2O, also called brushite). The dihydrate form is the standard pet-food and human-food grade ingredient because of its better processing handling and consistent mineral bioavailability profile.

Commercial DCP is produced by reacting phosphoric acid (H3PO4) with calcium hydroxide (Ca(OH)2) or calcium carbonate (CaCO3) at controlled pH 4–5 to favor dihydrate crystallization per standard mineral-premix industry references. The phosphoric acid feedstock is typically food-grade thermal-process material rather than the lower-grade wet-process acid used for fertilizer manufacture, which carries higher fluoride and heavy-metal contaminant loads. Per AAFCO 2024 and FDA 21 CFR 184.1217 GRAS affirmation, food-grade DCP is an accepted pet food and human food ingredient. The calcium-only alternative discussion is covered on our calcium carbonate explainer.

AAFCO calcium and phosphorus minima and maxima

Per AAFCO 2024 Official Publication canine maintenance nutrient profile, dietary calcium minimum is 0.5 percent and maximum is 2.5 percent on a dry-matter basis; phosphorus minimum is 0.4 percent and maximum is 1.6 percent. For canine growth and reproduction, the calcium minimum increases to 1.0 percent (with the same 2.5 percent maximum) and phosphorus minimum increases to 0.8 percent. Large-breed puppy formulations carry an additional AAFCO 2020 provision capping calcium at 1.8 percent and phosphorus at 1.6 percent to attenuate orthopedic developmental disease risk per Hazewinkel 1985 (J Nutr) and subsequent large-breed-growth literature.

Feline minima differ modestly per AAFCO 2024 feline maintenance nutrient profile: calcium minimum 0.6 percent, maximum unset; phosphorus minimum 0.5 percent, maximum unset. Per NRC 2006 Nutrient Requirements of Dogs and Cats and AAFCO 2024, the calcium-to-phosphorus ratio target is 1:1 to 2:1 across all life stages, with the upper bound (more calcium than phosphorus) avoiding the inverse-ratio pattern that drives secondary nutritional hyperparathyroidism. Dicalcium phosphate’s native Ca:P ratio of approximately 1.3:1 sits comfortably within the AAFCO band, which is why it is the workhorse combined mineral premix.

Bioavailability and absorption framework

Per Heaney 1989 (J Bone Miner Res) mineral bioavailability framework and standard nutrition references, dietary calcium bioavailability varies by salt form. Calcium citrate has the highest fractional absorption (~35 percent in pH-neutral conditions), calcium carbonate has lower absorption (~25–30 percent, pH-dependent and reduced with proton pump inhibitor co-administration), and dicalcium phosphate sits in the middle (~25–30 percent). Per Recker 1985 (N Engl J Med) and follow-up canine work, DCP calcium absorption is adequate for AAFCO-complete formulations.

Phosphorus from DCP is highly bioavailable (~80–90 percent fractional absorption per NRC 2006), substantially higher than phytate-bound plant phosphorus (~30–50 percent without phytase enzyme co-supplementation). This positions DCP as the primary phosphorus source in pet food, since phosphorus needs to track calcium addition closely to maintain the 1:1 to 2:1 ratio. Phytate-bound phosphorus from plant ingredients contributes additional phosphorus mass but at substantially lower bioavailability; formulators typically rely on DCP for the AAFCO-target phosphorus, with plant phosphorus as supplemental mass. The bioavailability framework overlaps with our selenium explainer trace-mineral context and our chelated-mineral discussion.

Fluoride and heavy-metal contaminant context

Per FDA-CVM mineral feed ingredient monitoring and historical pet-food industry references, the phosphoric acid feedstock for DCP manufacture matters for contaminant profile. Food-grade thermal-process phosphoric acid produces low-contaminant DCP suitable for pet food and human food. Wet-process phosphoric acid (used for fertilizer manufacture from phosphate rock with sulfuric acid digestion) carries higher fluoride content and may carry elevated cadmium, arsenic, and uranium contamination depending on the rock source. Pet-food-grade DCP is sourced from food-grade thermal-process supply chains.

Fluoride content in DCP-supplied pet food is generally below the threshold of concern for adult dogs and cats but has been the subject of historical industry discussion about cumulative fluoride exposure in dry kibble. Per AAFCO 2024 and FDA-CVM 2009 guidance, fluoride in commercial pet food is not regulated to a specific upper limit, but quality-conscious manufacturers source low-fluoride DCP supply. The cumulative-exposure question intersects with bone-meal-supplied phosphorus and the broader mineral premix supply chain. The mineral framework overlaps with our discussion of chelated vs inorganic mineral premix on our selenium explainer.

How KibbleIQ scores dicalcium phosphate

The KibbleIQ Dry Kibble Rubric treats dicalcium phosphate as a neutral mineral premix signal — expected presence in essentially every AAFCO-complete formulation. The rubric does not award credit or penalty for DCP per se. The rubric flags formulations where DCP is the sole calcium source in a high-meat-content formulation that ought to deliver substantial calcium from bone-containing protein meals (chicken meal, salmon meal, lamb meal carry 12–26 percent ash), as this suggests the named-species protein meal mass is lower than the label implies. The rubric awards modest credit for formulations using DCP alongside chelated trace minerals (zinc proteinate, copper amino acid chelate, manganese proteinate) over inorganic-only mineral premix.

To check the mineral profile of your dog’s food, paste the ingredient list into the KibbleIQ analyzer. For peer mineral context, see our calcium carbonate explainer, potassium chloride explainer, selenium explainer, manganese explainer, and our zinc, copper, and iron supplement explainers. For methodology context, see our published methodology.