How to backup iphone contacts without losing the old ones?

Of course itunes will delete the old data if you sync your iphone with itunes! You should put your iphone on itunes manual management, which lets you drag and drop what you want onto your iphone without syncing. do as the following: Connect your iphone to computer and launch itunes⟶find iphone under the "Devices" category in the left panel⟶check the "Summary" tab on the right⟶ click "Manually Manage" ⟶ "Apply". Well if you don’t wanna go through the troubles just get a iphone transfer to do all the backup thing

as all we know , iTunes doesn’t allow you to sync contacts from iPhone to iPad directly，and bluetooth can do nothing to transfer too. Now I share my experience: you need a USB cable with the device can configure cantact in itunes .Using a third-party software is a quick way export the contacts from iPhone to computer and then restore the files. For more ,search “how to transfer or backup iPhone contents to PC” or “how to transfer or backup iPhone contents to Mac”

Or you can just use icloud to backup your phone to just make sure on iphone in your iCloud settings you have backup on and contacts selected sign into icloud.com then whenever you need then on device there their or on a comp. If you need more help let me know im traveling so on and off with connection atm

First of all try using iTunes, it is designed by Apple for creating backup. In case it fails then you can make use of iCloud for backing up all the crucial files. For more security of files and avoiding loss of backup you should make use of iPhone backup tool for creating iPhone backup sms, contacts, phonebook, videos, music, photos etc.

thank you for your supplement.