Calculating the price before HST is added

I've always sold my photo calendars with "taxes in" to make it easy for my customers. However, when doing the invoices/receipts, I need to calculate the price before HST (Ontario/Canada tax), so that when the HST is added, the final price is what the customer paid.

I found this website that makes it easy and I thought I'd share.

http://hstcalculator.ca/ontario