When you take insulin, not all of it works at once. Insulin on board, also called active insulin or residual insulin, is the amount of insulin still working in your body after a dose. It's not just a number—it's the reason your blood sugar might drop hours after eating, even if you didn't eat again. This concept is critical for anyone using rapid-acting insulin, whether through injections or an insulin pump. Ignoring insulin on board can lead to double-dosing, which causes dangerous lows. Many people think if their blood sugar is high, they need more insulin—but if there's still active insulin from earlier, adding more can be risky.
Insulin sensitivity factor, also known as correction factor, tells you how much one unit of insulin lowers your blood sugar. Insulin duration, the time insulin stays active (usually 3 to 5 hours for rapid-acting types), works with insulin on board to predict your next move. These aren’t just technical terms—they’re tools. If your insulin duration is 4 hours and you took 2 units 2 hours ago, about 1 unit is still active. That’s half your dose still working. Many diabetes apps and pumps calculate this automatically, but knowing how it works lets you spot errors or adjust when tech fails.
People managing diabetes with insulin often struggle with unpredictable highs and lows. Sometimes it’s not about food—it’s about forgetting how much insulin is still in the system. A study from the American Diabetes Association found that nearly 40% of severe hypoglycemic events in pump users happened because of unaccounted insulin on board. You don’t need to be a math expert. Just learn your personal insulin curve. If you take insulin at lunch and your sugar drops at 4 p.m., that’s not a mystery—it’s insulin on board doing its job. Track it. Adjust it. Don’t guess.
Insulin on board also changes with activity, stress, or illness. Exercise can make insulin work faster. Fever can slow it down. That’s why one-size-fits-all settings fail. Your insulin on board isn’t static. It’s dynamic. And that’s why understanding it gives you real control. You’ll stop blaming yourself for low blood sugar and start making smarter decisions.
Below, you’ll find real-world guides on how to calculate insulin on board, how to use it with different insulin types, and how to avoid common mistakes that lead to dangerous lows. Whether you’re on a pump, multiple daily injections, or just starting out, these posts give you the practical tools to manage your insulin smarter—not harder.
Insulin stacking-giving rapid-acting insulin too soon after a previous dose-can cause dangerous low blood sugar. Learn how to avoid it with safe dosing intervals, real-world examples, and practical prevention tips.
