Apple’s iPhone Duo went on sale on 23 October, and for the first time an iPhone opens up into a 7.6-inch screen. That’s lovely for video and multitasking. It also means every app on your phone now has to cope with two very different screens: the 5.4-inch outer display when it’s closed and the much bigger inner one when it’s open.
I make small, focused iPhone apps, and I’ve spent the last few weeks updating them for the new hardware. Nine of them now support iPhone Duo. They all work the same way they always have: they’re quick, they don’t show ads, they don’t need an account, and your data stays on your phone.
Here’s what’s ready, grouped by what you’d actually use them for.
In the kitchen
The kitchen is where the bigger screen makes the most sense to me. Unfold the phone, prop it up on the worktop and you can actually read the numbers from a step away.
Recipe Scaler
Recipe Scaler resizes a recipe when you change the number of servings. Doubling a cake, halving a stew for two, or scaling cookies up to 48 for a bake sale all take a couple of taps.
- Scan recipes with the camera. Point it at a cookbook page, a printed recipe or a screenshot, and it reads the ingredients in for you to check.
- Sensible results. You get fractions you can measure, not “0.333 cups”. Small amounts stay precise and bigger ones round to clean numbers.
- Edit as you go. Add, change or remove ingredients, with volume, weight and count units.
Cook’s Converter
If you cook from American, British and European recipes, you’ll know the “how many grams is a cup of flour?” problem. Cook’s Converter answers it.
- Volume: teaspoons, tablespoons, fluid ounces, cups, pints, quarts, millilitres and litres
- Weight: grams, kilograms, ounces and pounds
- Temperature: Celsius, Fahrenheit and every Gas Mark from ¼ to 9
- Cups to grams for 50+ ingredients, based on each ingredient’s density, because a cup of sugar doesn’t weigh the same as a cup of flour
Tip for iPhone Duo: iOS 27 brings Split View to iPhone Duo, so you can open Recipe Scaler and Cook’s Converter side by side on the inner screen. Scale the recipe on one side and convert the awkward measurements on the other.
Air Fryer Timer
Air Fryer Timer turns oven instructions into air fryer settings. Type in the oven temperature (°C, °F or gas mark) and the cooking time, and it shows the adjusted temperature and time as you type.
It uses the usual rule of thumb: drop the temperature by 20°C (25°F) and cut the time by about 20%. Every air fryer is a bit different, so it also reminds you to check your food halfway through. You can save favourite recipes and open them with Siri Shortcuts.
At the gym
My Workout Plan
Most workout apps want a subscription and a profile before you’ve done a single rep. My Workout Plan doesn’t.
- Build your own plans with any exercises you like
- Set targets for sets, reps, weight or timed holds
- Log each set as you go, with a tick for every completed set and a progress bar for the session
- Look back at past workouts, which save automatically
There’s no account, no subscription and no cloud sync. Your training log lives on your phone.
On the road and travelling
Fuel Calculator
Fuel Calculator is built for UK drivers. It works out how much a journey will cost, how many litres you’ll use and your cost per mile.
- Imperial or metric: miles and MPG, or km and L/100km
- Journey log with mileage, fuel price, efficiency and notes
- CSV export through the share sheet, handy for mileage expense claims or your own spreadsheet
- Works offline, with UK default values so you’re not starting from scratch
Worldwide Tip Calculator
Tipping customs change a lot from one country to the next. Worldwide Tip Calculator gives you a suggested tip based on where you are, covering 25+ countries.
- Country presets with a short note on local tipping etiquette
- Split the bill between up to 20 people, with the tip and total shown per person
- Your own percentage if you’d rather set it yourself
- Local currency symbols shown automatically
For freelancers and small businesses
Simple Invoice Creator
Simple Invoice Creator is for anyone who needs to send a professional invoice without signing up to another monthly service.
- Quick invoices with automatic numbering and totals that update as you type
- Saved clients you can load in one tap
- 0% or 20% VAT with the tax broken down for you
- Print-ready PDFs with line items, tax, totals and payment terms
- Send it however you like: email, WhatsApp, Google Drive or any other app
It doesn’t need an account or an internet connection, and nothing gets uploaded anywhere. The bigger inner display on iPhone Duo is also a nicer place to check the line items before you hit send.
Just for fun
Paws and Leap
Paws and Leap is a tap-to-jump runner starring a black and white cat. The cat runs on its own, and you tap to jump over obstacles across 10 themed worlds, from a garden all the way to outer space. Each world gets faster and adds new obstacles.
There are 200 levels, and you earn up to three stars on each one depending on how many mistakes you make. The first world (20 levels) is free. A single one-off purchase unlocks the other nine. There are no ads and no subscriptions.
What Would You Rather
What Would You Rather has 1,000 “would you rather” questions, from silly to surprisingly deep. Shake the phone or tap the screen for a new one. It works offline, so it’s ideal for road trips, parties and family nights.
The app already uses a split-screen layout with one option on each half, so it suits a phone that unfolds into a bigger screen you can pass around the table.
Why these apps all work the same way
Every app on this list follows a few rules I care about:
- No ads. Nothing popping up while you’re mid-recipe or mid-workout.
- No accounts. You open the app and use it.
- Your data stays on your device. No tracking and no cloud sync you didn’t ask for.
- They do one job properly. Each app solves one problem and keeps out of your way.
Frequently asked questions
What is iPhone Duo?
iPhone Duo is Apple’s first foldable iPhone. It has a 5.4-inch outer display and a 7.6-inch inner display. It was announced in September 2026 and went on sale on 23 October 2026, running iOS 27.
Which of these apps support iPhone Duo?
All nine apps in this post have been updated with iPhone Duo support: Recipe Scaler, Cook’s Converter, Air Fryer Timer, My Workout Plan, Fuel Calculator, Worldwide Tip Calculator, Simple Invoice Creator, Paws and Leap, and What Would You Rather.
Do I need an iPhone Duo to use them?
No. They all run on any iPhone with iOS 16.4 or later. Most of them also run on iPad, Apple silicon Macs and Apple Vision Pro.
Do the apps have subscriptions?
No. None of them use subscriptions. Paws and Leap is free to start, with one optional purchase to unlock the rest of the game.
Do I need to create an account?
No. None of the apps ask you to sign up, and your data stays on your device.
Get them on the App Store
You can find all of my apps, including these iPhone Duo-ready ones, on my App Store developer page. If you’ve got an iPhone Duo and something doesn’t look quite right on either screen, let me know. I’m still tuning things for the new hardware and I’d love to hear how you’re using them.
