Zero logging. Zero timers. Cycle-synced fasting that adjusts your window based on where you are in your cycle — and how you actually felt today. One 30-second check-in. The AI handles the rest.
The eFood 2025 meta-analysis confirmed what circadian biologists have argued for years: when you eat matters as much as what you eat — and static schedules ignore the hormonal reality of your body clock.
Other fasting apps give everyone the same schedule and ask you to track everything yourself. That's not freedom — that's more tracking. Circafast adapts your window daily from a 30-second check-in. You rate how you felt. It figures out the rest.
Every other fasting app is a timer with a subscription. Circafast is a coach that pays attention — to how you feel, and to your cycle.
No other fasting app does this. Circafast adjusts your fasting window based on where you are in your cycle — automatically. Follicular phase? You can push harder. Luteal phase? We cap you at 16:6 so you're not fighting your hormones. One toggle. Your cycle, respected.
Works with or without AI coaching. Add your last period date in Settings — that's it. Perimenopause mode available.
One 30-second check-in per day — rate your energy, mood, and difficulty. The AI reads your pattern and adjusts tomorrow's window. No food diaries. No calorie counting. Nothing.
The AI explains every decision in plain English. "I moved your window earlier because your energy scores dip on long evening fasts." No black boxes. Ever.
One toggle and the AI is gone. No coaching, no suggestions, no "you should try 18:6." Just your schedule, your call.
No coaching, no check-ins, just a timer. Use Circafast as a pure fasting tracker — nothing more, nothing less.
Your data, your call. Delete everything in one tap — no support ticket, no waiting period, no dark patterns to navigate.
16:8 → 18:6 → 20:4, automatically when you're ready. Not on a fixed schedule — based on how you're actually feeling.
They're timers with a subscription fee. None of them adapt to your cycle. Circafast is $4.99/month — and it actually learns you.
| ⚡ Circafast | Zero | Fastic | Simple | |
|---|---|---|---|---|
| Price | $4.99/mo | $9.99/mo | $79.99/yr | $59.99/yr |
| Adaptive fasting protocol | ✓ | ✗ | ✗ | ✗ |
| Cycle-synced fasting 🌙 | ✓ | ✗ | ✗ | ✗ |
| Daily logging required | ✗ | ✓ | ✓ | ✓ |
| AI that learns your rhythm | ✓ | ✗ | ✗ | ✗ |
| Check-in takes <30 seconds | ✓ | ✗ | ✗ | ✗ |
| Free trial | 7 days | 7 days | varies | 7 days |
The stuff worth actually knowing before you start.
Why I Built This
I'm 19. I got tired of fasting apps that felt like homework — logging meals, counting every bite, running a marathon of inputs just to get a protocol that didn't even know I existed.
I built Circafast because I wanted something that actually paid attention. Not just my fasting window, but how I'm sleeping, how my energy is doing, and — for the women in my life — where they are in their cycle.
This isn't an app for people who want to optimize for an algorithm. It's for people who want a coach that actually knows them.
The monthly plan is $4.99/mo. But if you're in early, there's a better deal:
$29.99 once, lifetime access, no monthly fees ever.
— of 100 spots claimed
Zero logging. Cycle-aware. Transparent AI. Built by a 19-year-old who was tired of fasting apps that made everything feel like homework. $4.99/month — or $29.99 lifetime while spots last.