“Rule” is just what the community calls it — a Juicebox heuristic for thinking about pre-meal timing. Divide a BG by 10 for a starting lead time in minutes.
Enter any BG and see what the Rule of 10 would suggest for a starting pre-bolus window. This is a way to feel how the heuristic responds to different numbers — a learning tool, not a prescription.
The Rule of 10 is a mental shortcut for pre-bolus timing — how far in advance of a meal insulin is given. Instead of trying to remember a fixed number like "15 minutes" for every situation, the rule scales the lead time to the BG reading itself.
A higher BG gets a longer lead time, because there's more room for insulin to start working before food absorbs. A lower BG gets a shorter lead time — because glucose is already close to a floor, and insulin that's too far ahead of food can drop it too low.
For reference, published clinical studies of rapid-acting insulin recommend a fixed 15–20 minute pre-meal window. The Rule of 10 outputs roughly track that window for mid-range BGs, and deliberately shift shorter or longer at the extremes.
The Rule of 10 is a community-developed heuristic that came out of the Juicebox Podcast, not a published clinical guideline. It's shorthand — a way to translate the general principle "higher BG needs more lead time; lower BG needs less" into a number you can do in your head. It is not a rule from an endocrinology journal, a CDE training manual, or a medical association.
The actual clinical evidence on pre-bolus timing points to a fixed 15–20 minute window for rapid-acting insulin before a meal. The foundational studies are Cobry et al. (2010, Diabetes Technology & Therapeutics) and Luijf et al. (2010), both randomized crossover trials in people with T1D on pumps. Both found that bolusing 15–20 minutes before eating produced significantly lower post-meal glucose peaks than bolusing at the start of the meal or after. Slattery et al. (2018, Diabetic Medicine) systematically reviewed this evidence and concluded the same.
So why does the Rule of 10 exist on top of that? Because "15–20 minutes" is a single number applied to every situation. The Rule of 10 is a way to adjust around that window based on where a BG is starting from — shorter than 15 min at the low end, longer at the high end. It's a refinement of the clinical anchor, not a replacement for it.
If you're already elevated before a meal, insulin has more time to start working before food pushes glucose higher. A longer lead time lets insulin get out ahead of the carbs.
If you're already near the floor, giving insulin too far ahead of food can drop you low before the meal arrives. A shorter lead time leaves room to eat before insulin peaks.
Fixed numbers like "always wait 15 minutes" ignore where your BG actually is right now. The Rule of 10 adjusts the lead time to the situation without adding complexity.
Nobody's pre-bolus timing is "BG ÷ 10" forever — it's a starting point. The real learning happens in the CGM trace after the meal, and any lasting change is worked out with a care team.
The Rule of 10 only addresses timing — when to give the insulin. It doesn't tell you how much insulin to give, and it doesn't factor in whether your BG is rising or falling.
Two readings of 140 mg/dL are not the same situation. One may be rising fast from a snack an hour ago; one may be drifting down from a correction. The Rule of 10 produces the same 14-minute lead time for both — because that's not what it's trying to solve.
It also assumes a specific kind of insulin. The heuristic is built around standard rapid-acting insulin analogues — Humalog (lispro), Novolog (aspart), Admelog, Apidra. Ultra-rapid insulins like Fiasp and Lyumjev peak meaningfully faster, so applying the same lead times to them can put insulin ahead of food in ways the rule doesn't anticipate. Regular (short-acting) insulin peaks much later and would need significantly longer windows. Inhaled insulin (Afrezza) works on a different curve entirely.
That's why this is one of three pieces, not the whole picture. It handles the before — when to bolus. The during — where BG is actually heading — is the 30•60•90 Forecast. The after — reading your CGM trace once the meal plays out — is its own topic. Each does one job.
Scott and Jenny have covered pre-bolus timing across multiple series. Start here.
Pre-Bolusing: The Juicebox Way →