The effective 4.5% cashback on Amex Platinum Charge right now is a tempting option for large upcoming tax bills.
With B2Bpay's 2.2% fee for example: $100k tax payment = $2,200 fee = $1,595 after tax with a 27.5% tax rate = 450k Amex MR points = $4,500 credit on the card (can use it to cover a personal purchase to get full benefit) = roughly $3k 'profit'.
Alternatively 450k MR points = 225k QF/SQ miles = 0.7 cents/mile.
Normally I'd go for air miles but with 1.5 million SQ expiring in two years and millions more Amex and QF points already, I'm tempted to use the cash back option.
What to do ...
Thanks for laying it out so clearly - I'd never considered cash back option before but current promotion looks quite enticing - do my calculations make sense?
1) For $1000, you'd get 4500 AMEX points (Platinum) under current promotion, which translates to a cash back of $45, or in effect, 2 cents / point value
2) The pure financial decision (putting aside other considerations such as points accumulated and cash in hand considerations), is how this equation measures up to spending $19.50 / $1,000 (pre-tax figure using bluechain pre-GST rate of 1.95%), plus obtaining 2225 FF points.
3) Therefore, the financial decision depends on what value you think you can use your FF points for --- ie, if you calculate that on average, you get 2 cents / point value on FF points, then you'd be better off using cash-back during this promotion, and roughly, you'd want to get over 3 cents / FF point value to consider not using the cash-back (since @ 3 c / pt, 2225 pts = $66.75, minus $19.50 bluechain surcharge).
4) The equation changes slightly depending on if the $45 cash back is used for personal or business repayments (maybe 2.75 c / pt would be the equivalent value then?)
