Tandem Control-IQ: How It Works, Features, and Latest Updates

Key takeaways:
- Control-IQ is an insulin algorithm or calculator used in Tandem's t:slim X2 and Mobi insulin pumps.
- Control-IQ adjusts basal insulin delivery every five minutes to prevent highs and lows and increase time in range.
- Automatic correction boluses can be delivered once per hour if blood sugar is predicted to rise above 180 mg/dL.
Tandem's automated insulin delivery (AID) system is the combination of Control-IQ plus one of the company's two insulin pumps: either the t:slim X2, introduced in 2018, or the smaller Mobi, which became available in 2023 plus a Dexcom or Abbott continuous glucose monitors (CGM).
The system uses an algorithm built into the pump that adjusts basal insulin delivery and gives automatic correction boluses. Based on CGM readings and a 30-minute prediction, Control-IQ can increase basal insulin if blood sugar is predicted to rise above 160 mg/dL and deliver correction bolus doses, up to once per hour, if glucose is expected to rise above 180 mg/dL.
Control-IQ is compatible with the Dexcom G6/G7 CGM. The t:slim X2 can also use the Abbott Freestyle Libre 2 Plus CGM.
How does Control-IQ work to keep people in range?
Control-IQ employs a hybrid closed-loop algorithm, which requires the user to first enter pump settings including basal profile, insulin-to-carb ratio, and insulin sensitivity factor.
The system uses a range of targets based on the time of day or expected activities, including:
- Automated basal rate adjustment during the day (including after meals): The system targets a range of 112.5-160 mg/dL.
- Automated basal rate adjustment at night: The algorithm becomes more aggressive at night and tries to arrive at 112.5-120 mg/dL by morning.
- Exercise activity mode: Users can manually choose a higher target range of 140-160 mg/dL to avoid low blood sugar during or after exercise.
- Sleep activity mode: Users can set programmed sleep schedules with a target range of 112.5–120 mg/dL (or you can enter this mode manually).
The system works to keep users in range (between 70-180 mg/dL) based on a combination of strategies. When the predicted CGM value in 30 minutes is:
- Above 160 mg/dL, basal insulin rate increases
- Above 180 mg/dL, a correction bolus is given up to once per hour
- Between 112.5-160 mg/dL, default user settings are maintained
- Below 112.5 mg/dL, basal insulin decreases
- Below 70 mg/dL, basal insulin is turned off
Users are still expected to bolus for meals. Control-IQ will give about 60% of a full correction bolus with a target of 110 mg/dL. These boluses occur in addition to the automatic basal rate and can help move blood sugar back into range even when meal boluses are missed.
What the research says
The FDA cleared Tandem’s Control-IQ algorithm in 2019 after clinical trials found the system to be safe and effective. Here's how Control-IQ compared to using the same pump and CGM without the algorithm:
- Time in range was 2.6 hours per day better with Control-IQ (70% vs. 59%), with users spending 2.4 fewer hours per day above 180 mg/dL.
- Average A1C was 0.3% lower with Control-IQ.
- Average blood glucose was 14 mg/dL lower with Control-IQ (156 mg/dL vs. 170 mg/dL).
A 2021 study of 9,000 people with diabetes using Control-IQ found within two weeks of starting the system, time in range (70–180 mg/dL) increased by more than 10%. The average time in range for participants after 12 months of using the system was 74%.
A 2024 study tested the ability of a modified version of Control-IQ designed for a lower target range of 90–130 mg/dL. The results showed that both time in range and time in tight range (70–140 mg/dL) improved by more than 3%. The same study tested a delayed bolus feature meant to reduce hypoglycemia (low blood sugar).
The study reported both the lower target range and the late bolus feature improved blood sugar management, though the lower target led to a small increase in blood sugar readings below 70 mg/dL.
How much does Control-IQ cost?
For users of non-Tandem pumps, the cost to switch is $999. A limited offer for $199 for the Mobi is available to Tandem users who purchased a t:slim X2 between July 1, 2023 and December 31, 2023. For users of the t:slim X2 who bought their pump before July 1, 2023 and have 12 months or more on their warranty, the cost of the Mobi is $999.
Many health insurance plans cover AID systems for people with diabetes but check your plan as individual coverage may vary. Without insurance, the t:slim X2 costs around $4,000 while the Mobi costs roughly $8,000. The warranty period for Tandem pumps is four years.
Learn more about Control-IQ and automated insulin delivery here: