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?
What's happening here?
Fast-acting insulin does not work instantly. It takes about 10 minutes to start working, peaks (has the most change per minute) around one hour after bolus, and can last up to six hours in your body.
Similarly, food doesn't all digest at once. Carbohydrates will cause blood sugars to rise faster than insulin causes it to decline, which means blood sugar can rise before insulin reaches peak effectiveness. Fat and protein absorb slower than insulin works and will slow down digestion of carbs as well.
For carbohydrate-only meals:
- Eating immediately after bolusing may cause an early spike, as insulin isn't working yet.
- Pre-bolusing (giving insulin 10–30 minutes before eating) may better match insulin action to carb absorption.
- Waiting too long to eat after a bolus may increase the risk of an early low.
For high-fat meals:
- Fat slows digestion, so a pre-bolus might increase the risk of an early low before food absorbs.
- Bolusing when you start or after you start eating will let food absorption start before insulin kicks in.
- Blood sugar may rise later and stay elevated longer, so you may need to split your bolus.
Applying this to your own life
When eating, look at how the timing of insulin boluses for different meals result in blood sugar changes similar or different to what you notice in this chart. You can do this by looking at a CGM or testing your blood sugar every 30 minutes after you start eating.
As you make observations, keep notes on what different bolus times result in with different meals. Use that information to make decisions when eating similar types of food in the future.