Act 1

Try Any Scenario

Enter any BG reading and choose a trend arrow. Both outputs update instantly. Try different combinations to see how the math responds — this is a learning tool, not a prescription.

Step 1 — Enter a BG to Explore

mg/dL

70120180250300

70–99 mg/dL

Below Target

100–140 mg/dL

In Range

141+ mg/dL

Above Target

Step 2 — Choose a Trend Arrow

Rule of 10 + Trend — Timing

—

Minute Lead Time

30•60•90 — Scenario BG

—

mg/dL to Explore

↕

Enter a BG above to explore the rules

For educational use only. Not a medical device. Not medical advice. Always verify with your healthcare team before adjusting insulin therapy. Full disclaimer →

Act 2

Understand the Concepts

⏱

Rule of 10 — Timing

Divide any BG reading by 10. The result shows roughly how many minutes of lead time the rule would suggest. A rising trend adds to that; a falling trend subtracts.

📐

30•60•90 Rule — Dose

Your trend arrow indicates where glucose is heading. Add or subtract 30, 60, or 90 mg/dL to get a scenario BG that reflects momentum — not just the current number.

Rule of 10 — the math:

Pre-bolus minutes = BG \div 10 (+ trend adjustment) BG 180 mg/dL + steady \to 18 min | BG 180 mg/dL + ↑ \to 21 min | BG 90 mg/dL + \to \to 9 min

BG: 80 mg/dL

minutes (steady)

BG: 120 mg/dL

minutes (steady)

BG: 200 mg/dL

minutes (steady)

30•60•90 — what each arrow suggests:

Arrow	What's Happening	Rate	Scenario Adjustment
↑↑	Very fast rise	>3 mg/dL / min	+90 mg/dL
↑	Fast rise	2–3 mg/dL / min	+60 mg/dL
↗	Slow rise	1–2 mg/dL / min	+30 mg/dL
→	Steady	<1 mg/dL / min	No adjustment
↘	Slow fall	1–2 mg/dL / min	−30 mg/dL
↓	Fast fall	2–3 mg/dL / min	−60 mg/dL
↓↓	Very fast fall	>3 mg/dL / min	−90 mg/dL

A BG of 120 mg/dL with a ↑↑ arrow is a completely different picture than 120 mg/dL with a flat arrow. The number alone doesn't tell the story — the trend is the missing context.

Act 3

What Happened After the Meal?

The real learning happens after you eat. Your CGM trace is feedback. Tap any pattern below to understand what it might be telling you — and what to explore adjusting.

📈↘

You saw this

BG spiked, then came back down on its own

Timing ▾

The insulin eventually caught up and brought glucose back to range — which means the dose was probably about right. But the spike tells you the insulin wasn't working yet when the carbs arrived. The insulin didn't get enough of a head start before it had to compete with the meal.

What to explore Try a longer pre-bolus next time for a similar meal and BG level. The Rule of 10 window could be extended by a few minutes, or the dose given sooner.

📉

You saw this

BG went low within about an hour of eating

Timing ▾

The insulin peaked before the carbohydrates were fully absorbed — insulin was ahead of the food. This is usually a timing issue rather than a dose issue, because the glucose eventually came up (from the meal) rather than staying low.

What to explore Try a shorter pre-bolus window next time. The Rule of 10 may be suggesting more lead time than your particular insulin speed and meal type require.

📊

You saw this

BG went up gradually and kind of stayed there

Dose ▾

The glucose rose slowly and steadily but didn't come back down on its own — suggesting the pre-bolus timing may have been reasonable, but there wasn't quite enough insulin to cover the full impact of the meal. A small correction was likely needed later.

What to explore The timing concept looks reasonable here. The exploration is around dose — whether the carb count was accurate, whether fat/protein extended the rise, or whether the ICR needs revisiting for this type of meal.

📈📈

You saw this

BG shot up and stayed up

Timing + Dose ▾

When glucose rises steeply and doesn't come back, both timing and dose are worth examining. The insulin wasn't ahead of the carbs (timing) and there wasn't enough of it (dose). These two problems can compound each other — insulin that starts late also appears to work less efficiently because it's fighting a steeper rise.

What to explore Both a longer pre-bolus window and a review of the dose may be worth exploring — ideally separately, one change at a time, so you can learn what each variable is doing.

⏰📉

You saw this

BG went low 2–3 hours after eating

Dose ▾

A low that arrives well after a meal — rather than within the first hour — typically points to too much insulin rather than timing. The carbohydrates were already absorbed and the insulin kept working past them. This is less likely to be a pre-bolus timing issue and more likely a dose or carb-count issue.

What to explore Consider whether the carb estimate was too high, whether fat/protein slowed absorption (making the carb bolus run ahead of the food), or whether the ICR needs adjusting for this meal type.

"If you eat and your blood sugar shoots straight up, comes back down and comes right back to normal later — you didn't give the insulin enough time to get working before it had to fight with the carbs.

If it goes up very gradually and kind of stays up there and never comes back — your pre-bolus was probably pretty good, you just didn't use quite enough insulin.

If it shoots up and stays up — not enough insulin and not enough pre-bolus.

These aren't hard and fast rules — they're just great places to start figuring out what's happening."

Scott Benner

Juicebox Podcast — Episode 476: Common Sense v. Fear

Estimators

Guides

Series & Collections

Site Links

Shop

Educational Use Only

Pre-Bolus Timing & Adjustment

Try Any Scenario

Understand the Concepts

What Happened After the Meal?

Pre-Bolusing on the Juicebox Podcast