A bolus is insulin taken for a specific job, right now — as opposed to basal insulin, which runs quietly in the background all day. The two classic jobs: a meal bolus, covering the carbs you are about to eat, and a correction bolus, bringing down a glucose reading that is higher than you want. Rapid-acting insulins used for bolusing typically start working in about 15 minutes, peak around one to two hours, and hang around for three to five.
Meal boluses are usually sized using an insulin-to-carb ratio, and corrections using a correction factor — both of which are personal numbers worked out with your care team. On a pump, a bolus is delivered by the device on demand; on injections, it is the mealtime pen or syringe dose.
A few concepts that orbit bolusing:
- Insulin on board (IOB): bolus insulin from the last few hours that is still active — stacking corrections on top of it is a classic route to a low.
- Extended or split boluses: pump features that stretch delivery out for slow meals like pizza.
- Timing relative to the meal matters, because insulin and food race each other — see pre-bolus.
How much, when, and how to adjust are exactly the questions your care team helps you calibrate — the answers are different for every body.
