For CEWS there is no need to recalculate the CPP and EI as neither figure into the accounting for this subsidy. If you are starting to claim from Period 1 the law is very clear that you will have to figure the daily rate based on the pre-Covid period of January 1 to March 17 and use this as the base. If the employees are salaried it is relatively easy to calculate a weekly equivalent and then use that amount for each week of claim. If the pay varies due to bonuses or hours worked you will have to recalculate based on hours for each week of each Period. Yes, it is a lot of extra work but for 75% (in the first four Period) as a subsidy it is worth it.

I agree with Alwyn, it is a lot of work but must be done.  I am fortunate in one way with our monthly paid employees I do a spreadsheet for each employee that breaks it down by days because we have so many different pay rates and groups like regular, overtime, shop, travel etc.  So now to do the CEWS I draw lines on the spreadsheets breaking it down by the CEWS weeks required, do the rate calculations (including vacation pay) and plug those numbers into the CEWS Spreadsheet that they provide.  It takes me a full day to do it but at least I know I have the amounts down to the penny just in case CRA decides to do an Audit!.  Good luck with whatever you choose but like Alwyn said it is worth it.

Just to clarify, Alwyn ... and hopefully to help some people avoid a mistake I've seen in some CEWS calculations.  When you are filling in the claim form online, there are lines asking about the employer share of CPP and EI for furloughed employees.  Any amounts you enter on these lines get added to your basic CEWS.

Unfortunately, "furlough" isn't a word that gets used much, and I've seen several employer claim these amounts when they weren't eligible for them.  The extra CEWS subsidy which equals the employer's share of CPP and EI is ONLY FOR EMPLOYEES YOU PAID WITHOUT EXPECTING THEM TO WORK OR USE UP VACATION OR BANKED TIME.  This is an extra bonus for employers who weren't actually able to use their employees' services but decided to keep paying them so they wouldn't need to go on EI.

Like the main CEWS calculation, the extra CPP/EI calculation is absolutely driven by calendar weeks, so calculations will be needed if you have any other type of pay period and are making the claim.