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What is the lifespan of a series of currency?
In general, currency has no expiration date. Specifically, in Canada, the Bank of Canada has been issuing banknotes since 1935, and these are still considered legal tender, even though they don't look much like the modern banknotes.  Before that, Canadian chartered banks issued currency, and these also still have value. However, there are a few things to note.  First of all, with currency of that age, it often has more value as a collector's item than the face value.  So spending it at a store would be foolish. Second, store clerks are not experts in old currency, and will not accept a bill that they do not recognize.  If you want the face value of your old currency, you may need to exchange it for modern currency at a bank. Having said all that, there are certainly cases where currency does expire.  Generally this happens when a country changes currency.  For example, when the Euro was introduced, the old currencies were discontinued.  After a window of exchange, the old currency in many cases lost its value.  So if you have some old French Franc notes, for example, they can no longer be exchanged for Euros. These types of events cannot be predicted in the future, of course, so it is impossible to say when, if ever, the Canadian currency you have today will lose its spending value in Canada.