This calculator implements a weight-based unfractionated heparin protocol — the kind printed on hospital anticoagulation nomograms — to give the initial IV bolus, starting infusion, and the corresponding pump rate. It is built for nurses, pharmacists, and anticoagulation clinics initiating a heparin drip.
How it works
Two simple per-kilogram rules drive the starting dose:
Bolus (units) = bolus per kg × weight
Infusion (units/hr) = rate per kg × weight
A widely used venous thromboembolism (VTE) nomogram uses an 80 units/kg bolus and an 18 units/kg/hr infusion; acute coronary syndrome protocols often use lower figures (60 units/kg bolus, 12 units/kg/hr) with explicit caps. If you enter optional caps, the tool clamps the bolus or infusion to that maximum and labels it as capped — protecting very heavy patients from excessive dosing.
The pump rate then follows from the bag concentration:
Rate (mL/hr) = infusion units/hr ÷ concentration (units/mL)
A common premixed bag of 25,000 units in 250 mL is 100 units/mL.
Adjusting the infusion
The starting infusion is only the beginning. Heparin is titrated to a target aPTT or anti-Xa level using your institution’s adjustment table. Recheck the level about 6 hours after starting and after every rate change, then step the rate up or down per the nomogram. This tool plans the initial dose only — it does not perform the aPTT-based titration. Always verify doses with a pharmacist or anticoagulation service. All calculation runs locally in your browser.