Mike,

Interesting question...

In your second example, the meal still cost $100... no doubt about it... you just received something in addition (the miles) as a result.

However, in your first example you are only being charged $80 for the dinner. In essence, a 20% discount. No different than using a 20% off coupon. I would never think of charging my company more than I actually PAID for the meal or service.

So, I would only expense the $80. That is the only way I could live ethically with the decision.

However, the easy solution is to just ask what they expect and desire. They may tell you to expense the full amount as that discount benefit is yours for using your personal card (as are the miles).\

William