Flip Timer & stopwatch vs Acid Interval
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Flip Timer & stopwatch
This app offers a full-screen digital timer with a unique flip animation to visualize time progression. It also includes a stopwatch for tracking activities like workouts, study sessions, and work. Customize reminder sounds and background audio for an immersive experience.
- Full-screen digital timer
- Flip animation for time visualization
- Countdown timer
- Stopwatch functionality
- Customizable reminder sounds
- Background sound options
- Keep screen on for progress viewing
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Flip Timer, A full-screen digital timer. Countdown, flip animation allows you to feel the passage of time; Stopwatch, record your sport, fitness, work, study and so on. - Swipe up or slide down to set the countdown duration - you can set up timed reminder sound - Focus on the work, you can set the background sound, so you immersed them. - Keep the screen on, You can view the progress of time at any time
Acid Interval
This focus timer offers a visually unique approach to deep work, moving away from traditional interfaces. It provides customizable timers and engaging visual feedback to help users stay on task, even with the screen off. The app prioritizes a distraction-free experience with no account or data syncing required.
- Unique visual interface
- Customizable timer intervals
- Engaging animation mechanisms
- Screen-off notifications
- No account or data sync
- Phone lock compatibility
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A focus timer worth looking at. Most focus timers look like a spreadsheet with a countdown in it. This one is built the other way round. A single enormous numeral, bleeding off the edge of a field of acid green. Behind it, a mechanism that moves in time with the clock and never drifts. Rings that bounce, breathe, ripple inward, or pass momentum down a Newton's cradle. A square whose perimeter burns like a fuse, four seconds a side, for box breathing. When you start a session the whole field inverts to black and the numbers light up like something switched on behind them. Tap anywhere to start. Swipe to change the color. You never have to open a menu. 25/5, 50/10, 90/20, or count up. The classic pomodoro, longer ultradian blocks, or open-ended flow when you don't want a deadline. Timed properly. Built on timestamps, not ticks. Lock your phone, switch apps, come back: it is exactly where it should be. It tells you when you are done, even with the screen off. No account. No sync. No data leaves your phone. ACID INTERVAL PRO One payment unlocks all eight mechanisms, all ten colorways, and custom interval lengths. The timer itself is free and always will be.
Screenshots
Verdict
The clearest difference is ads: Acid Interval at none against Flip Timer & stopwatch's shown. Acid Interval also leads on rating (5.0 vs 4.6) and update cadence (every 2 weeks vs every 3 months). Flip Timer & stopwatch's advantage is ratings volume (7.6K vs 1) and device support (3 vs 1). On price, in-app purchases and monetization model there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. Flip Timer & stopwatch sells 3 one-off in-app purchases and Acid Interval sells 1 one-off in-app purchase. Whichever you choose, the download price is not the number that matters.
Acid Interval holds the better App Store score, 5.0 against 4.6. That said, the two scores are not equally well evidenced: Flip Timer & stopwatch has 7.6K ratings behind it against 1, so its average is the more settled of the two.
Flip Timer & stopwatch ships an update every 3 months, Acid Interval every 2 weeks. The most recent releases landed on October 24, 2026 and October 22, 2026 respectively.
| Parameter | Flip Timer & stopwatch | Acid Interval |
|---|---|---|
| Price | Free | Free |
| Rating | 4.6 (7.6K ratings) | 5.0 (1 ratings) — better |
| Positive reviews | 68.6% of reviews | — |
| Number of ratings | 7.6K — better | 1 |
| Update frequency | Every 3 months | Every 2 weeks — better |
| Ads | Yes | No — better |
| In-app purchases | Yes | Yes |
| Monetization | Free with in-app purchases | Freemium |
| Devices | iPhone, iPad, iPod — better | iPhone |
| Requires iOS | 15.0 — better | 17.0 |
| Further details — not scored | ||
| Size | 46 MB | 1 MB |
| Age rating | 4+ | 4+ |
| Developer | 俐 马 | Preston Carr |
Customer experience
Flip Timer & stopwatch
Acid Interval
Bugs and requests
Flip Timer & stopwatch
Reported bugs
3 issues- Timer randomly stops counting down
- Unable to stop/reset timer once started
- Ads prevent user from interacting with timer
Requested features
4 requests- Add option to set timer in hours/minutes/seconds
- Implement repeat/loop functionality for timer
- Allow custom alarm/notification sounds
- Improve landscape mode support
Acid Interval
Not enough reviews yet to summarise bugs or requests.
In-app purchases
Flip Timer & stopwatch
- Remove Ads$0.99
- All the skins$0.99
- Pro Version$1.99
Acid Interval
- Acid Interval Pro$2.99
Questions
Is Flip Timer & stopwatch free?
Is Acid Interval free?
Which has better reviews, Flip Timer & stopwatch or Acid Interval?
Do Flip Timer & stopwatch or Acid Interval have ads?
Which is updated more often, Flip Timer & stopwatch or Acid Interval?
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