This answer applies to 2015 and later tax years only.
Before the optimizer runs, we automatically allocate donations based on income. After the optimizer has run, you can choose who claims what.
Donations can be split with your partner or carried forward to use in future years. In the examples, the words “you” and “your” refer to the active return.
When you reduce your claim, the amount of the reduction will get applied to the carryforwards table. If you want your partner to claim the amount instead, switch to their return and add the amount.
When you increase your claim, the amount of the increase will first get pulled from the carryforward table and then from your partner’s claim.