Temp Basal Simulator

For pump users: see how adjusting your basal rate around exercise affects blood glucose.

Insulin pumps deliver basal insulin as small, continuous pulses of fast-acting insulin. A temporary basal rate lets you reduce or increase this delivery for a set period of time.

This chart is designed to help you visualize how adjusting your basal rate before, during, and after exercise changes insulin delivery and blood glucose — especially when combined with food and the glucose-lowering effect of exercise itself.

Pay attention to:

What happens when you reduce basal too late before exercise?
What happens when you reduce it too much or too early?
How does food interact with the temp basal effect?

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

What's happening here?

Insulin pumps deliver basal insulin as rapid micro-pulses of fast-acting insulin, unlike MDI users who inject a slow-acting basal insulin once or twice a day. This means pump basal can be adjusted in real time — increased, decreased, or suspended — to respond to changing circumstances like exercise.

A temporary basal rate reduces or increases this ongoing delivery for a set period. Because each micro-pulse of fast-acting insulin has the same absorption curve as a bolus, the timing of the rate change matters as much as the magnitude.

Why timing matters

Fast-acting insulin from a temp basal change takes 15-30 minutes to start reducing delivery and 60-90 minutes to reach peak impact
Setting a temp basal at the start of exercise is often too late — the insulin from the minutes just before exercise is already absorbed and active
Starting a reduced basal 60-90 minutes before exercise gives the change time to take effect before activity begins

What happens when basal is reduced

Less fast-acting insulin is delivered over time, so the ongoing pull on blood sugar decreases
Blood sugar tends to drift upward if basal is reduced for long enough
The exercise-driven glucose uptake partially offsets this rise, but the balance is different for every individual

What happens after exercise

Returning to normal basal while insulin sensitivity is still elevated can cause a drop
Some people maintain a reduced basal for 1-2 hours after finishing to account for lingering sensitivity
Food eaten post-workout will also have a smaller insulin requirement than usual

Applying this to your own life

Temp basals require experimentation. Start with a modest reduction (50-70%) beginning 60-90 minutes before exercise, and track what happens to blood sugar during and after.

Keep notes on:

What time before exercise you set the temp basal and how blood sugar responded
Whether the exercise-driven drop was blunted, eliminated, or whether you went high instead
How long after exercise your blood sugar continued to trend down, and whether a reduced basal post-workout helped