You should check your blood sugar one to two hours after the start of a meal. The American Diabetes Association recommends testing within this window and aiming for a reading below 180 mg/dL (10.0 mmol/L) for most people with diabetes. The clock starts at your first bite, not when you finish eating.
Why the One-to-Two-Hour Window
Blood sugar doesn’t spike the moment you eat. Your body needs time to break down food, absorb glucose, and move it into your bloodstream. For most people with diabetes, glucose peaks about 75 minutes after starting a meal. A study of insulin-treated patients found that 80% of post-meal glucose peaks occurred within 90 minutes of the first bite, with similar timing after breakfast, lunch, and dinner.
Testing at one to two hours catches this peak or its tail end, giving you the most useful snapshot of how your body handled the meal. Test too early and you might miss the spike entirely. Test too late and your reading may have already dropped back toward your baseline, hiding a problem.
One Hour vs. Two Hours
A one-hour test and a two-hour test tell you slightly different things. At one hour, you’re more likely seeing the actual peak, which reveals how sharply a particular food raised your glucose. At two hours, you’re seeing how well your body is clearing that glucose from the bloodstream, which reflects your overall insulin response.
For most people with type 1 or type 2 diabetes, the two-hour mark is the standard checkpoint. The ADA’s 2026 Standards of Care define the post-meal target as below 180 mg/dL measured one to two hours after the beginning of the meal. Your care team may set a tighter target depending on your situation, but this is the general benchmark.
If your numbers are consistently under 180 at two hours but you suspect they’re spiking higher before that, testing at one hour (or around 75 minutes) can reveal hidden peaks. This is especially useful when you’re trying to figure out which specific foods or portions cause trouble.
Gestational Diabetes Has Different Rules
If you have gestational diabetes, your targets are stricter and testing timing matters more. Common targets are below 140 mg/dL at one hour or below 120 mg/dL at two hours after meals. A recent meta-analysis found that targeting the one-hour reading of 140 mg/dL significantly reduced the risk of having a larger-than-expected baby compared to using the two-hour target alone. However, pushing the one-hour target even lower (to 120 mg/dL) increased the risk of preterm delivery without additional benefits to birth weight. Your OB or endocrinologist will tell you which window to use, and it’s worth sticking to it precisely.
How Meal Composition Shifts the Peak
Not every meal follows the standard timeline. A bowl of white rice will spike your glucose faster than a steak with vegetables, and the testing window should reflect that.
High-fat meals cause an earlier glucose rise that peaks around two hours, then gradually declines over five hours. High-protein meals are the opposite: they produce a slower, more sustained rise that peaks around three and a half hours after eating and can keep glucose elevated for five hours. This means a protein-heavy dinner like grilled chicken and cheese might look fine at the two-hour mark but cause high readings later in the evening.
If you notice unexplained high readings hours after eating, the protein and fat content of your meal is a likely culprit. For these meals, an additional check at three or four hours can be informative.
Fingerstick vs. Continuous Glucose Monitor
If you use a continuous glucose monitor (CGM), keep in mind that it reads glucose from the fluid between your cells, not directly from your blood. This creates a lag of 5 to 20 minutes compared to a fingerstick. When your blood sugar is rising quickly after a meal, your CGM may show a lower number than a fingerstick would at that exact moment. When glucose is falling, the reverse happens: the CGM may read slightly higher.
This lag is small enough that it rarely changes clinical decisions, but it’s worth knowing if you’re comparing a CGM reading at exactly one hour post-meal to a fingerstick target. The CGM’s real advantage is that it shows you the full curve, so you can see exactly when your personal peak occurs rather than guessing.
Building a Useful Testing Routine
A single post-meal reading doesn’t tell you much on its own. What makes the data useful is pairing it with a pre-meal (fasting or before-eating) reading so you can see how far your glucose rose. A jump from 95 to 160 mg/dL tells a different story than a jump from 150 to 210, even though the first reading is technically within range at both checkpoints.
If you’re testing to understand your patterns rather than just hitting a target, try checking before and then 1 to 1.5 hours after several different types of meals over a week or two. Note what you ate, the portion size, and any activity afterward. This paired approach turns isolated numbers into a practical map of how your body responds to specific foods, which is far more actionable than a single post-meal check in isolation.