Bolus Timing Simulator

Move the slider to see how insulin timing relative to meal start affects blood glucose.

When you eat, your blood sugar rises. When you take insulin, your blood sugar falls. That sounds simple, but timing of insulin in relation to eating impacts how blood sugars change during that process.

This chart is designed to help you visualize how insulin absorption and food digestion overlap over time with carbs or high fat meals. By adjusting when insulin is given relative to when food is eaten, you can see how different timing strategies may change the shape of your blood sugar curve.

Pay attention to:

What happens when insulin peaks before the carbs hit?
What happens when carbs rise before insulin peaks?
How does adding fat to a meal change the curves?

For educational purposes only. This simulator is a visual learning tool — not a medical device or dosing calculator.

What's happening here?

Fast-acting insulin starts working about 10 minutes after injection, peaks around 60-90 minutes, and stays active for up to 6 hours. It does not follow a sharp on/off curve — it ramps up slowly, reaches a peak, then tapers off gradually.

Food digests at a different rate than insulin works. Carbohydrates raise blood sugar faster than insulin can pull it down. Fat and protein slow that absorption considerably.

When you bolus early (pre-bolus)

Insulin begins working before carbs are digested, which can blunt or prevent the post-meal spike
Bolusing too far ahead can cause blood sugar to drop before food absorbs, especially with lower-carb or mixed meals
Pre-bolusing works best with fast-digesting, carbohydrate-heavy meals

When you bolus late or at meal start

Carbs absorb while insulin is still ramping up, which often causes a spike before insulin brings it back down
For high-fat meals, a later bolus may better match the slower digestion curve
A late bolus rarely causes the same early low risk as a pre-bolus does

Applying this to your own life

Track what happens with different bolus timing for the meals you eat most often. A CGM makes this easy — look at the curve 1-3 hours after eating. Over time, you will develop a feel for how much lead time each type of meal needs.

Keep notes on:

Which meals benefit from a 15-30 minute pre-bolus
Which meals cause an early drop when pre-bolused
How the curve differs between carb-heavy and high-fat meals