Charitable donations over $200 per year are automatically eligible to carry forward and apply in the next 5 years, to maximize the refund amount.
They are refunded to you at 15% on the first $200 and 29% on amounts over $200, so if you are donating any amount more than $200 on a yearly basis and you can afford to wait for the refund, it's beneficial for you to apply / use all of your available charitable donations on one tax return every 5 years.
Note that donation receipts can only be claimed once, and up to a maximum claim amount of 75% of your income.
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