How does LastSip work?

LastSip helps you find your sweet spot: the latest time you can enjoy caffeine without messing with your sleep. It includes a 45-minute ramp-up phase as caffeine kicks in, then tracks how your body clears it based on your sensitivity. It works backward from your bedtime to find your ideal cutoff.

What's the science behind it?

LastSip uses a science-based approach:

  • Absorption: Caffeine takes about 45 minutes to reach full strength.
  • Decay: Your body clears it gradually. Every half-life, the amount drops by half.
  • Multiple drinks: Each drink gets its own curve, and they all add up by bedtime.

Behind the scenes, LastSip simulates this 45-minute absorption phase, applies exponential decay based on your sensitivity, and checks if you'll be under your threshold at bedtime.

Caffeine sensitivity

The sensitivity slider controls how long caffeine stays in your system.

  • High sensitivity means your body clears it slowly, so your cutoff is earlier.
  • Low sensitivity means faster clearance, so you get more flexibility.

This changes your half-life between about 2 and 10 hours.

Sleep Priority Mode

Sleep Priority lowers your bedtime threshold from 50 mg to 35 mg. It helps if you're sensitive to caffeine, dealing with anxiety, or focused on getting deeper sleep.

When this mode is active, you can also set a custom sleep threshold in the Settings menu, allowing you to fine-tune your caffeine limit anywhere between 10mg and 100mg.

Planning Mode

Planning Mode is a powerful simulator that lets you map out your entire day's caffeine intake. Instead of calculating a single cutoff time, it tells you if your full plan will leave your caffeine levels in a good place by bedtime.

Simply toggle the icon on the main screen to enter Planning Mode, add all the drinks you plan to have, and see if your plan is "Safe" or if it needs adjustments.

Different result scenarios
  • Safe: You're clear to sip.
  • Warning: You’ve passed the ideal cutoff, but it may still be okay.
  • Stop: Too close to bedtime or already over the limit.

If you're cutting it close, LastSip might suggest a gentler drink that still fits.

Add and manage drinks

You can log drinks you already had or plan ones for later. Tap Add for a quick entry or Add More to queue several. You can track up to 10 drinks. Tap any drink to edit its time, amount, or type.

Caffeine visualization

The chart gives you a snapshot of your day:

  • Solid line shows your caffeine level
  • Red line marks your sleep threshold
  • Dotted lines show future drinks
  • Gray dashed line suggests your ideal cutoff

Use it to see when caffeine builds up and when it clears.

Custom beverages

Can’t find your drink? Use the Custom Beverage option to name it, enter the caffeine amount, and save it for later. You can keep up to 20.

Accuracy

The model is built on science, but real life varies:

  • Your metabolism may be faster or slower
  • Food can affect absorption speed
  • Drink values are sometimes estimates

Use your result as a guide, and adjust based on how you feel.

Data privacy

Your data stays on your device. Nothing is uploaded or tracked. We use Plausible Analytics to monitor general site usage—no ads, no cookies, and no personal information collected.

What’s different in the mobile app?

The LastSip mobile app offers a streamlined, offline-first experience with enhanced native features:

  • Use the app offline — no connection required
  • Receive smart cutoff reminders
  • Enjoy native haptic feedback and smooth mobile interactions
  • Easily share your results with built-in mobile sharing

It's a one-time $1.99 download for users who want LastSip in their pocket, even when offline.