Can I claim ITC on GST already claimed as expense on my income tax return?

I already claimed as expense GST and PST on business expenses on my tax return. I now realised that I can claim ITC on GST I paid. Can I still do it? I understand that in the future I should claim as expense (on income tax return) an amount I paid plus PST and leave out GST. Then GST should be claimed as ITC? Am I correct?
Many thanks.

If you are a business you have a GST number and collect GST on your sales. The GST you pay on your business expenses are netted off against the GST you collect and remit to the government.

The GST is a flow through tax and it is worth dollar for dollar as an input tax rebate.

As a tax deduction the GST paid would give you back less than $0.18 on the dollar; assuming your business was taxable and has a small business tax rate.

You would have to re-file your business return to remove the GST paid from your business expenses if you re-file your GST return.

The only issue is how much GST are we talking about? If you had $2,000 in expenses the GST paid would only be worth $100 and you would owe about $18 more in business taxes. I do not think I would bother re-filing in that case. You might incur interest charges on re-filing of your business income taxes and who knows what else.

In the future keep the GST paid as an input credit and not as a business expense. Depending on the amount your business would net out it might be worthwhile to re-file your GST & income tax returns; but I suspect not.

Claim the GST paid as an ITC (assuming you're filing the detailed version of the GST report each period).

You'll need to file an amended return to change what you've already filed, you can't claim twice (as a deduction and as an ITC), but you can amend your return to remove the GST deduction.