Part 5 – Exercise Insulin on Board (IOB) Calculator to Estimate Hypoglycaemia Risk for Type 1 Diabetes (flip to landscape if using a phone)

Simple explanation

When you take insulin, it does not disappear straight away. It slowly fades over several hours. This calculator estimates how much insulin may still be in your body at the planned start of activity. You enter your body weight, insulin doses, and the date and time they were given. The calculator works out how much of each dose may still be active and adds them together.

The bar and colour show how exposure rises from very low to extremely high risk. It does not predict glucose levels. It helps people understand how insulin exposure changes over time and may affect activity risk.

Practical interpretation

In simple terms, the higher the circulating insulin exposure, the higher the risk of hypoglycaemia during activity and the more carbohydrate may be needed to maintain glucose levels.

This IOB scale can be used as a practical starting framework. Very low and low exposure generally suggest lower risk. As exposure rises through medium and high bands, carbohydrate needs typically increase and exercise planning becomes more important.

These values are starting points only. Individual responses vary depending on fitness, activity type, timing, recent food, environment and personal insulin sensitivity. The main aim is to observe what happens at different exposure levels and learn from the pattern.

Detailed explanation

This calculator estimates current circulating insulin exposure from recent bolus doses. Each dose is converted into units per kilogram (U/kg).

The model assumes larger doses peak later and have longer duration. Anchor points used in the model are:

• 0.05 U/kg → peak ~1 hour, tail ~4 hours
• 0.10 U/kg → peak ~1.5 hours, tail ~6 hours
• 0.20 U/kg → peak ~2 hours, tail ~7 hours
• 0.30 U/kg → peak ~2.5 hours, tail ~8 hours

Intermediate doses are interpolated between these points. A curvilinear decay function estimates the remaining fraction over time. The remaining insulin from each dose is summed to estimate total circulating insulin exposure.

The display uses a continuous colour gradient across the current GNL exposure scale:

• 0.00 = V.Low
• 0.02 = Low
• 0.04 = Med/Low
• 0.06 = Med
• 0.08 = Med/High
• 0.10 = High
• 0.12 = V.High
• >0.14 = E.High

Carbohydrate suggestions are a practical learning framework based on current glucose, exercise type and estimated insulin exposure. They are not a precise prediction engine and should be used to observe patterns, learn and adapt. For glucose above 15.0 mmol/L, the 0 g carbohydrate output is a simplified starting assumption and assumes ketones are less than 1.5 mmol/L.