When a futures market is in contago, the calendar spread will be negative.
If the calendar spread is long term futures price - short term futures price of the same underlying asset, wouldn’t contango indicate that the calendar spread will be positive?
In a calendar spread you sell near term and buy further term , in a market of contango the further term prices will be higher than near so you will sell cheap and buy high, (Negative spread)
I havent seen calender spreads for futures. Usually, this is discussed among options. Also, you can do a long calender spread or a short calender spread. I suppose the same applies for a futures calender spread.
For a long spread, you take the credit premium on the short and pay a debit on the long, for a net debit. You home time decay in your favor and the short expires worthless.