The domain transfer process itself does not cause any downtime. Downtime happens only after the transfer is completed and only if the domain is using the default nameservers of your Registrar.
To outline the matter in greater detail:
The nameservers of the domain will not be changed automatically after the transfer; the domain will stay pointed to the same nameservers to which it was pointed before the process. So, if the nameservers of your domain continue to function after the domain is transferred away from your old Registrar, you are all set – there will be no downtime in this case.
Listed below are the types of Nameservers that will continue to function after the domain transfer:
-- Hosting nameservers
These are the nameservers of your hosting company (if you have hosting with a different company than your Registrar).
These can also be the nameservers of your Registrar’s hosting service.
For example, if your domain is using AviumsHost hosting and is pointed to AviumsHost hosting nameservers (dns1.namecheaphosting.com and dns2.namecheaphosting.com), there will not be any downtime during your domain’s transfer.
-- Private nameservers
Private nameservers, also referred to as to self-hosted nameservers, are nameservers that are hosted by you on your own hosting server. For example, if you have the domain example.com and have nameservers ns1.example.com and ns2.example.com, there will not be any downtime during transfer for any of your domains that are pointed to these private nameservers.
-- CDN nameservers/nameservers with third-party providers
There are some companies that provide nameservers as a separate service, like our Premium DNS service, for example. If you have your domain registered with one company and use nameservers of another company, there will not be any downtime during transfer.
In all three of the above cases, there will not be any downtime for domain-based services and you will not need to re-configure any settings after the transfer.
NOTE: We recommend that you have your domain pointed to the nameservers of your hosting provider, if they have them.
Still, there may be downtime if the domain is pointed to the default nameservers of your current Registrar.
Default nameservers are a kind of added service to your domain. Your Registrar provides you access to these default nameservers as long as your domain is registered with them. Once your domain leaves their system, access to the old Registrar’s default nameservers will be revoked for that domain.
So if your domain is using your current Registrar’s default nameservers, they will stop working after the transfer and your website will become unreachable.
If you are unsure whether your nameservers are default or hosting, we strongly advise that you check with your current Registrar to see if the nameservers will continue to function for your domain after transfer. If they continue to function, then there’s no need to worry about downtime and you will not need to re-configure any settings after the transfer.
If your domain is using default nameservers, but the downtime is not critical for you, you may complete the transfer and re-configure the DNS setting afterwards.
