(a) Yes. (b) No.
(a) No, do not panic. That is never a good idea.
However it is important to know your options. Tactics can make a huge difference when you have missed a deadline. Let me give you an example.
If you miss your tax filing deadline in Canada and there is tax owing you are charged a penalty based on the balance owing at the deadline date. Seems cut and dry but it is actually flexible in ways people often don’t consider. In Canada a person or a company is often remitting taxes to several departments and for multiple deadlines at the same time. A business can be remitting GST installments and corporate tax installments and payroll installments and because there is overlap between installment periods those installments can be tagged to different years or periods even when they are out of that period. What does this mean?
It means that a good tactical move is to look at all of the installments you have made and perhaps move them around like game pieces on a game board to meet each deadline in the best timing and amount to suit your needs. Let me illustrate.
If you had made a $5,000 GST installment June 15th for a December year end that was due the following March and also had a $5,000 income tax amount due related to the prior years income tax for December prior year end that was due the end of this June; which one of those two deadlines is more imminent and would be a smarter place to assign the $5,000 installment? It would be smarter to move it from GST to income taxes.
This kind of flexibility is often available and people are unaware of it and end up paying penalties unnecessarily. All of this is to illustrate that you should not panic when you miss a deadline. You should instead carefully analyze your options and make tactical moves to reduce the cost of a missed deadline.