T1D glossary

Basal insulin

Also called background insulin, basal rate, long-acting insulin.

Basal insulin is the steady background insulin that covers the body's needs between meals and overnight. It comes as a long-acting injection, or as a continuous drip of rapid-acting insulin from a pump. Its dose is tuned to overnight and fasting glucose. (ADA Standards of Care 2026, section 9; OpenAPS documentation)

Worked example

A pump might run 0.5 units an hour overnight; 8 hours of that rate adds up to 4 units. Someone on injections gets the same kind of background cover from one long-acting dose.

Related terms

• Bolus
• Dawn phenomenon
• Closed loop

Sources, quoted

• ADA Standards of Care 2026, section 9: “Basal insulin includes NPH insulin, long-acting insulin analogs, and continuous delivery of rapid-acting insulin via an insulin pump.”
• ADA Standards of Care 2026, section 9: “The long-acting basal dose is titrated to regulate overnight and fasting glucose.”
• OpenAPS documentation: “Basal - baseline insulin level that is pre-programmed into your pump and mimics the insulin your pancreas would give throughout the day and night”

Every quote above is checked against its source page before each update of this site; last checked 2026-10-06. The worked example is our own arithmetic. This page explains a term; it is not advice for a person's treatment.