With premium air fares up a great deal this year I was thinking the other day about how much I might theoretically spend on premium air travel and when I should bite the bullet and fly economy.

The conclusion I came to was that I will continue to buy premium air travel as long as the following three rules apply:
* the total price of the ticket is less than 100% of one month's income (after tax as I do not pay tax)
* the total premium over economy on a daylight flight operated by a non-stop service carrier is less than one month's income less rent
* the total price of all planned travel per year is less than 300% of one month's after tax income.

What is the maximum % of monthly income you would consider to spend on premium air travel?