Preoperative Fasting Intervals
Compares an elapsed fasting interval against the minimum for what was last taken, from the 2023 practice guidelines.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- What was last taken
- Clear liquids: water, pulp-free juice, carbonated drinks, black tea or…
- Hours since then, counted to induction rather than to the scheduled time
- 3 h
Result: 3 hours since clear liquids meets the minimum of 2
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Clear liquids
- Two hours. Water, pulp-free juice, carbonated drinks, black tea and black coffee qualify; anything with milk in it does not, and neither does alcohol.
- Breast milk, formula
- Four hours for breast milk, six for infant formula.
- Meals
- Six hours for nonhuman milk or a light meal; eight or more for fried or fatty food, or meat.
- Minimums, not targets
- Nothing by mouth after midnight is the practice this guideline was written against. Prolonged fasting is not safer, and it causes thirst, hypoglycemia, irritability and hypovolemia.
- The clock
- Runs to the moment of induction, not to the scheduled time. A delayed case does not extend a fast already served; it lengthens it.
- What is outside the table
- Emergency surgery, impaired gastric emptying, and glucagon-like peptide-1 receptor agonists. The intervals never guarantee an empty stomach.
What you enter
- What was last taken
- Hours since then, counted to induction rather than to the scheduled time
How this is calculated
American Society of Anesthesiologists Task Force on Preoperative Fasting. 2023 American Society of Anesthesiologists Practice Guidelines for Preoperative Fasting. Anesthesiology. 2023;138(2):132-151. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.