Note Maximum Registration Period and auto-renew grace period
Typically. you should expect the registration fee to add an additional year to your current renewal date. Keep in mind that the date at which you start the transfer, or the current renewal date, may result in no date extension.
For example, Google domains does not add an additional year if you transfer within 45 days of the current renewal date. Also, if you already at the maximum number of years that can be reserve for a domain, you won't see an increase.
Here's the full wording from the Google domains policy
Transfer during the auto-renew grace period
When you don’t renew a
domain, the registrar automatically renews the domain. Then, you have
an auto-renew grace period to cancel your domain registration. The
auto-renew grace period is about 45 days for .com and .net domains and
varies for other TLDs. When you cancel your registration, the
registrar provides a refund for the registration cost.
If you transfer a domain to Google Domains during the auto-renew grace
period, you won’t see an increase in the registration expiration date
when Google Domains adds a year because the transfer cancels the
previous renewal. To get a refund for the other year, contact the
Maximum registration period
In some cases, renewing the domain for the required one additional
year causes the domain to exceed the maximum registration period. In
these cases, you must wait until renewing for one year does not extend
the total registration period beyond the maximum allowed.