Personal Finance Canada

No, once you've contributed, your contribution limit goes down definitively, and it can only go up if you gain new contribution room because you had new income.

Let's make it appear with 2 counters, considering that John never receives any new room to make it clearer.

• At the beginning of the year 2021, John had a contribution limit and a deduction limit of $10,000 each.

CL : 10k

DL : 10k

• In April 2021, John contributed 2k.

CL : 10k-2k = 8k

DL : 10k

• In May 2022, John chose not to deduct his contribution off his 2021 income :

CL : 8k

DL : 10k

• In June 2022, John contributed 5k.

CL : 8k-5k = 3k

DL : 10k

• In May 2023, John chose to deduct all of his contributions off his 2022 income :

CL : 3k

DL : 10k - (2k + 5k) = 3k

You should not contribute more than your contribution limit, as you'll get a penalty (there is a 2k buffer, but you shouldn't count on it), and you should not deduct more than your deduction limit and what you have contributed, as you'll be reassessed by CRA.