If you’re on Multiple Daily Injections (MDI), you understand there are risks associated with injecting insulin multiple times at close intervals (known as insulin stacking). However, Insulin on Board (IOB) may not be a familiar term, but it is one of the most important factors of insulin therapy. Understanding IOB can provide you helpful insight into how much insulin is still working in your body, which can help reduce some of the risks of insulin stacking.1

In this article, we’ll go through what IOB is, why it’s important, and how it fits into your therapy.

What is IOB and why is it important?

IOB, also referred to as active insulin or bolus on board, is the amount of insulin that is still working in your body, but has not yet affected the glucose level (BG or CGM) from your previous bolus injection. When you inject rapid-acting insulin, the insulin typically starts working within about 15 minutes, takes 1–2 hours to peak, and then continues to work in your body for 2–5 hours. So injecting more insulin during this time period and not considering IOB can result in insulin stacking.1

Percentage of insulin injected decreasing over time
Figure shows the percentage of insulin injected decreasing over time. IOB starts when an insulin injection is given and ends when it is no longer lowering the glucose concentration in blood (BGM) and tissue (CGM).1

To simplify things, your healthcare provider may have cautioned you to be careful taking a correction bolus within 3–5 hours of your last injection to reduce insulin stacking. However, IOB can be a more accurate way to guide your insulin therapy. It can help you to determine a more accurate correction bolus as you will know how much insulin remains from previous bolus injections before you take more.

Knowing your IOB can help you in the following ways:1

  • Prevent hypoglycemia
  • Reduce insulin stacking
  • Help dose your injections more accurately
  • Provide confidence in administering a correction bolus

How do I make IOB part of my insulin therapy?

If you were to wait 5 hours between bolus injections, you could reduce, or avoid altogether, insulin stacking.1 The reality is you will likely have situations where you require another bolus of insulin before that time. This is where IOB can help. For example, if you want a snack 1 hour after your injection, and your blood glucose levels are within your target range, you should consider how much IOB is remaining. If you have a large amount of IOB you may want to reduce your injection amount, since you have insulin remaining, which has not yet lowered the glucose concentration in your blood (BGM) and tissue (CGM).

Aside from the time you take an injection, you should also check your IOB at the following times:1

  • Bedtime – a large amount of IOB may indicate blood glucose will decrease over night
  • When hypoglycemic – a large amount of IOB may indicate extra carbs are needed
  • Before driving – a large amount of IOB could indicate your blood glucose levels may decrease while driving
  • Before exercise/activity – a large amount of IOB may require extra carbs to prevent hypoglycemia

To understand how your IOB works, you will also need to know about the Duration of Insulin Action (DIA), also called insulin action time. While IOB shows how much insulin is remaining in your body from previous boluses, the DIA reflects the amount of time insulin lowers your glucose. It is important to work with your healthcare provider to help you determine your DIA, which may vary from person to person.1

mylife App with built in IOB feature

mylife App with built in IOB feature
mylife App with built in IOB feature.

While it is possible to calculate IOB manually, it can be difficult and inconvenient. The good news is, our mylife App has an IOB feature built in! Combined with other great features, including an electronic logbook and a bolus suggestion calculator, you can record your insulin injections, track your IOB over time, and calculate your insulin dose.

The mylife App is available for free at the Apple App Store and Google Play Store. It is recommended that you work with your healthcare provider to go through the initial setup and tailor the settings, including your DIA. Your healthcare provider can also help you understand when and how to deviate from the suggested bolus dose. Once you’re set up, you can check your IOB safely with the convenience of your mobile device.

Discover our product offerings to help people on multiple daily injections, including the mylife App.


The content is for informational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding bolus calculation, IOB and your therapy.

1 John Walsh, P.A. and Ruth Roberts, M.A., Pumping Insulin, 6th edition, Torrey Pines Press, 2017.