Hi Sasank,
Thanks for reaching out in Apple Support Communities. I understand that when you try to use the percent function in the Calculator app on your iPhone, it seems to be automatically choosing 10% as the value to calculate by. I use the Calculator app on my iPhone frequently; I'm happy to help with this. What you're describing sounds unexpected; I'd recommend trying these steps first:
If the behavior continues, I'd suggest removing the calculator app and reinstalling it:
- On your iOS or iPadOS device, touch and hold the app.
- Tap Rearrange Apps.
- Tap
in the upper-left corner to delete the app. - Tap Delete. Then on an iPhone X or later, tap Done. Or on an iPhone 8 or earlier, press the Home button.
If you have an Apple Watch, deleting an app from your iPhone also deletes that app from your Apple Watch.

- On your iOS or iPadOS device, go to the App Store.
- Search for the app. Make sure that you use the exact name of the app. Find the correct name of built-in apps.
- Tap
to restore the app. - Wait for the app to restore, then open it from your Home screen.
If you have an Apple Watch, restoring an app to your iPhone also restores that app to your Apple Watch."
Delete built-in Apple apps on your iOS 12, iOS 13, or iPadOS device or Apple Watch
Let me know what you find.
Best Regards.