IV Fluid Therapy Calculator for Dogs & Cats

By Dr Duncan Houston

Enter a patient's blood results, hydration status and clinical signs. The calculator recommends the best-fit IV fluid, calculates the fluid rate, plans shock boluses, and doses common bag additives and electrolyte corrections for the actual patient and bag size.

Patient & blood results

Patient

Species and weight drive every dose and rate below.

Species

Body weight kg

Clinical assessment

Perfusion comes before rehydration — these flags change the plan and the warnings.

Dehydration (physical exam) Perfusion deficit / shock signs (tachycardia, pale MM, prolonged CRT, weak pulses, dull) Neurological signs (seizures, tremors, stupor) Sepsis suspected Acute kidney injury / oliguria–anuria Coagulopathy / thrombocytopaenia Anorexic puppy / kitten

Ongoing losses ml/day

Vomiting/diarrhoea — estimate or weigh: 1 g of liquid = 1 ml of fluid.

Blood results

Leave anything you have not measured blank — it is simply skipped.

Na⁺ mmol/L

K⁺ mmol/L

Cl⁻ mmol/L

iCa²⁺ mmol/L

Total Ca mmol/L

Phosphate mmol/L

Glucose mmol/L

Lactate mmol/L

HCO₃⁻ mmol/L

Total protein g/L

Albumin g/L

PCV %

Rehydration plan

Replace 25–50% of the deficit over 4–6 h, then the remainder over 18–24 h.

Deficit in phase 1 % (25–50)

Phase 1 duration h (4–6)

Remainder over h (18–24)

Target Na⁺ mmol/L

Used for sodium corrections; defaults to the edge of the reference range.

Fluid bag size ml

Used to calculate bag additives (dextrose, KCl, hypertonic saline).

Reference ranges & stock (editable)

Na low

Na high

K low

K high

Cl low

Cl high

iCa low

iCa high

tCa low

tCa high

Glucose low

Glucose high

Phos low

Phos high

Hypertonic saline Na mmol/L

Base fluid Na mmol/L

Defaults follow the protocol notes; adjust to your analyser. The notes give 7% NaCl as 1155 mmol/L in the worked example (the fluid table lists 1283) — set to your stock.

Enter a body weight and blood results to generate a fluid plan.

How this veterinary fluid therapy calculator works

The calculator follows the standard stepwise approach to small-animal fluid therapy: correct perfusion first, then rehydrate, then cover maintenance and ongoing losses, with electrolyte corrections running alongside. It applies the core formula IV fluid rate = fluid deficit + maintenance + ongoing losses, where the dehydration deficit is % dehydration × body weight (kg) × 10 in ml, replaced 25–50% over the first 4–6 hours and the remainder over 18–24 hours, and maintenance is 132 × kg^0.75 ml/day for dogs or 80 × kg^0.75 ml/day for cats.

Fluid selection is driven by the blood results you enter. A balanced isotonic replacement crystalloid (Hartmann's or Plasmalyte 148) is the default; 0.9% NaCl is recommended for hypercalcaemia, hyperphosphataemia, hypochloraemic alkalosis and moderate-to-severe hyperkalaemia; and sodium derangements get a fluid matched to within 5–10 mmol/L of the patient's serum sodium, corrected no faster than 0.5 mmol/L per hour. Additives — potassium chloride, dextrose, hypertonic saline and phosphate — are dosed in millilitres or millimoles for your selected bag size, with maximum-rate safety checks such as the 0.5 mEq/kg/h potassium ceiling and the central-line rule for dextrose above 5%.

Built from published small-animal references including DiBartola's Fluid, Electrolyte and Acid-Base Disorders, Mazzaferro & Powell, Silverstein, and Creedon & Davis. Explore more free veterinary tools on ASK A VET™.

Fluid therapy FAQs

How do I calculate an IV fluid rate for a dog or cat?

IV fluid rate = fluid deficit + maintenance + ongoing losses. The dehydration deficit in ml is % dehydration × body weight (kg) × 10, replaced 25–50% over 4–6 hours and the remainder over 18–24 hours. Maintenance and estimated ongoing losses (vomiting, diarrhoea) are added on top.

What is the maintenance fluid rate for dogs and cats?

Maintenance is 132 × body weight (kg)^0.75 ml/day for dogs, and 80 × body weight (kg)^0.75 ml/day for cats. A linear alternative is 30 × kg + 70 ml/day. For a 25 kg dog that is roughly 1480 ml/day, about 60 ml/hour.

How do I calculate a dehydration fluid deficit?

Fluid deficit (L) = % dehydration × body weight (kg) ÷ 100. Estimate dehydration from the physical exam: tacky mucous membranes about 5%, skin tenting with dry membranes and CRT over 2 seconds 8–10%, sunken eyes and cold extremities 12% or more. An 8% dehydrated 25 kg dog has a 2 L deficit.

What is the shock fluid dose for dogs and cats?

Give 10 ml/kg isotonic crystalloid boluses IV, repeated while reassessing resuscitation end-points. If 50% of a shock dose (40 ml/kg in dogs, 30 ml/kg in cats) produces no improvement, consider adding a colloid or hypertonic saline bolus if not contraindicated.

How much potassium can I add to IV fluids?

Dose by serum potassium: from 20 mmol KCl per litre when K⁺ is 3.6–5.0 mmol/L up to 80 mmol per litre when K⁺ is below 2.0 mmol/L. Never exceed an infusion rate of 0.5 mEq/kg/hour, which caps the fluid rate for each bag concentration. Maintenance fluids typically get 10–20 mmol KCl per litre.

When does IV dextrose need a central line?

Dextrose concentrations above 5% are hyperosmolar and must run through a central line such as a jugular or drum catheter, never a peripheral catheter, because of phlebitis and thrombosis risk. 2.5% and 5% dextrose are peripheral-vein safe. To make 2.5%, add 50 ml of 50% dextrose to a 1 L bag after removing an equal volume.

How fast can serum sodium be corrected?

No faster than 0.5 mmol/L per hour in either direction. Correcting hypernatraemia too quickly causes cerebral oedema; raising sodium too quickly in hyponatraemia risks myelinolysis. Recheck electrolytes every 4 hours while correcting sodium.

Does this calculator replace clinical judgement?

No. It is decision support for veterinary professionals, built from published small-animal fluid therapy references. Doses must be checked against the individual patient, serial monitoring and your own hospital protocol.

About Dr Duncan Houston

Dr Duncan Houston is an emergency and GP veterinarian and the founder of ASK A VET™, the animal health platform for pet and farm animal profiles, health tracking, AI veterinary assistance and certified vet chat. He graduated with a Bachelor of Veterinary Science from the University of Sydney and has worked in emergency, general and mobile practice across Australia and Hong Kong. He built this calculator to make fluid plans faster, safer and consistent in busy clinics.