Least Stamps Combination Finder for Canada Post

Yes, while it is obviously more cost effective to put the exact value of stamps required on the envelope, there is no rule stopping you from putting a combined stamp value higher than what is required on the envelope. One instance where you may find yourself doing this is if you need to make the $2.61 rate and only have $0.80 stamps on hand. Four stamps would be $2.40 which is underpaying, and five stamps would be $3.20 which is overpaying. If you don't want to be bothered purchasing the remaining denominations to make up the $0.21, you can certainly just put that fifth $0.80 stamp on to bring the total to $3.20 and Canada Post will not complain one bit. But again, it is usually better to do exact values and avoid overpaying.

No, you can not. If you bring your completed envelope to the counter clerk to mail out and they notice undervalued stamps they will not accept the envelope until you've applied the required postage. If you don't have extra stamps to make up the difference, the counter clerk can accept cash and affix a printed label with the remaining postage for you. If you drop your underpaid envelope in one of the mail collection boxes, the postage discrepancy will be caught at the sorting facility and the envelope will be labeled insufficient postage and returned-to-sender.

A "P" stamp is worth the value labelled on a booklet or coil. So for example, right now a single "P" stamp can be purchased at the counter for $1.44 or you can purchase a booklet of 10 "P" stamps at a rate of $1.24 per stamp ($1.24 x 10). That $1.24 is the value of the "P" stamp. The $1.44 represents the $1.24 rate plus an invisible $0.20 surcharge for only buying one stamp at the counter, because it uses the counter clerk's time and Canada Post incentivizes people to buy the booklets of 10 to avoid the surcharge. So if you go in to mail one letter and buy a booklet to avoid the surcharge instead of buying one stamp, you've spent about nine dollars more than you planned on and that money is locked in to Canada Post now (the remaining nine stamps can only be used to mail a letter, it's not like Walmart will accept them as payment). So that's the reason for the surcharge, is to encourage larger value purchases at the counter. Something to note is when you are combining "P" stamps with denominated stamps ($0.32, $0.67, etc) to make up a larger postage rate, you should value the "P" stamps at their booklet rate ($1.24) NOT THEIR COUNTER RATE ($1.44). The counter rate is just that, for a single stamp bought at the counter. If you use the counter rate in your calculations for combining stamps, your math is going to be wrong and you will end up underpaying postage and it will be returned to you.