Garmin Connect IQ • Widget

Caffeine Tracker

How it works: the widget estimates your current caffeine level (mg/L), applies half-life decay over time, and predicts when you’ll drop below your sleep-safe threshold.

← Back to homepage Find your caffeine half-life View in Garmin Store

Note: the watch cannot measure blood caffeine. This is a model-based estimate using what you log, your body weight, and metabolism settings.

What does “mg/L” mean?

mg/L means milligrams of caffeine per liter. The app uses mg/L as a practical “concentration-like” score: it’s easier to interpret than total mg alone, because body weight influences how strong caffeine feels.

The same drink affects people differently
Body weight changes concentration
Concentration makes thresholds easier to understand

Widget showing current caffeine level in mg/L

The widget shows your current estimated caffeine level in mg/L.

Graph showing caffeine decay and thresholds

The graph shows how caffeine decays over time and when you drop below your sleep-safe threshold.

Important: This is an estimate. Garmin watches can’t measure caffeine in blood. The model is designed to be practical and useful, not medical-grade.

What the levels mean (thresholds)

Everyone reacts differently, but these thresholds work well as practical guideposts:

0.6 mg/L

Sleep

Sleep-safe target

A practical “aim to be below” level before sleep. Most people can fall asleep without issues at this level, while keeping sleep disruption minimal — even if you’re sensitive to caffeine.

1.0 mg/L

Stm

Stimulation starts

Around this level, many people begin to feel noticeable stimulation, such as increased alertness or reduced sleepiness.

5.0 mg/L

High

High level

A high caffeine level where side effects become more likely, including jitters, nervousness, or an elevated heart rate.

10.0 mg/L

Max

Very high level

Very high caffeine level associated with strong stimulation and a high risk of adverse health effects, including anxiety, tremor, and heart palpitations. Additional caffeine is likely to worsen symptoms.

Tip: If you’re very sleep-focused or sensitive, a lower sleep target (e.g., 0.6 mg/L) can be a useful goal. In Premium, you can set your own Caffeine threshold to match your tolerance.

Premium sleep recommendations & settings

The Last drink time recommendation is available in Premium. It helps you decide when you can take a specific drink and still keep your caffeine low enough for sleep.

Premium-only features in this section:
Last drink time • Caffeine threshold setting • Bed time buffer setting • Half-life presets • Custom drinks

Bed time

Your usual sleep time. By default, it’s taken from your Garmin settings. Premium uses Bed time as the reference point for sleep recommendations.

Bed time buffer (Premium)

A simple safety window before your Bed time. It exists for one reason: to prevent the app from recommending a small caffeinated drink too close to sleep.

Even if a tiny drink would technically keep you below your Caffeine threshold by Bed time, having caffeine right before sleep can still worsen sleep quality or make it harder to fall asleep.

In short:
Bed time buffer adds a “no-caffeine too close to bedtime” guardrail. It does not affect anything else in the model.

Caffeine threshold (Premium, default: 0.6 mg/L)

The sleep-safe limit Premium uses for recommendations. The app tries to ensure your predicted caffeine level at Bed time stays at or below this threshold.

If you’re sensitive or sleep gets worse → consider lowering the threshold
If you tolerate caffeine well and sleep is unaffected → you can slightly increase it

Caffeine half-life (Premium presets, default: 5 hours)

Half-life controls how fast caffeine decays (exponential decay). A shorter half-life clears faster; a longer half-life stays longer and pushes Last drink time earlier.

Premium half-life presets:
3 hours • 4 hours • 5 hours • 6 hours • 8 hours • 10 hours

Last drink time (Premium)

For each drink, Premium computes the latest time you can take it so that your predicted caffeine level at Bed time stays ≤ Caffeine threshold. Then it applies the Bed time buffer as a final guardrail, so the recommendation is never “too close” to sleep.

Depends on your current level, half-life, threshold, and Bed time
Also depends on the drink’s caffeine amount (especially for custom drinks)

Reminder: This is a model-based estimate — not a medical measurement.

Premium personalization

Premium unlocks advanced personalization so the model matches your habits and metabolism better:

Last drink time recommendation (Premium) — see the latest time for a drink so you stay below your sleep-safe threshold by bedtime.
Custom drinks & caffeine amounts (Premium) — add your own drinks with exact mg (e.g., Energy Drink 500 ml — 160 mg).
Adjustable caffeine threshold (Premium) — choose your sleep-safe limit (default 0.6 mg/L).
Bed time buffer (Premium) — avoid caffeine too close to bedtime (even if a tiny dose would still be below the threshold).
Adjustable caffeine half-life (Premium) — choose one of the supported presets below.

Supported half-life settings (Premium):
3 hours • 4 hours • 5 hours • 6 hours • 8 hours • 10 hours

Premium: add custom drinks so your logged caffeine matches what you actually drink.

Premium: choose a half-life preset to better match how fast you metabolize caffeine.

Computation algorithm (simplified)

Internally, the app keeps a running estimate of your current caffeine level and updates it whenever time passes or you log a drink. The model is based on exponential decay (half-life).

Step 1: Start with the last known level

The app stores your last computed caffeine level and its timestamp.

Step 2: Let it decay over time (half-life)

When the widget updates, the level is reduced based on how much time has passed since the last update:

Decay formula:
levelNow = levelPrev × 0.5^(Δt / halfLife)
Where Δt is time elapsed (in the same units as halfLife).

Step 3: Add newly logged drinks

When you log a drink, its caffeine amount (mg) is converted into a level increase using your body weight, and added on top of the current decayed level:

Update rule:
levelNow = levelNow + drinkDelta
drinkDelta is derived from the drink’s caffeine (mg) and your configured weight-based normalization.

Step 4: Predict “sleep-safe time”

To estimate when you’ll fall below a chosen threshold, the app solves the decay equation for time:

Sleep-safe prediction:
timeToThreshold = halfLife × log2(levelNow / threshold)
If levelNow ≤ threshold, timeToThreshold is 0 (already below).

Background updates:
The app refreshes your estimate automatically (e.g., every 5 minutes), so your current level stays accurate without manual refresh.