1 Leptin is a powerful and influential hormone produced by your fat cells. 2  It plays a key role in regulating energy intake and energy expenditure.
(Upgrades are not available on fares in the L, T, and U range, however, which are the most deeply discounted.) To calculate the price of an upgrade, Delta charges a dollar amount per 500 miles. $50: Up to 500 miles. $75: 501-1000 miles. $100: 1001-1500 miles.
That's how this latest hike played out: Delta raised fares only on tickets purchased within seven days of departure, which essentially targets the last-minute business traveler. It was nothing radical; the hike varied from just $4 to $10 round-trip (depending on the route) but these things do add up.