Quote from optioncoach:
Well calendars and credit spreads both have limited risks so there not a catastrophe with either strategy per se. What matters is how much risk you put in the position. Someone doing 10 credit spreads could have less risk than someone doing 50 calendars.
That is why with any position you cannot put 100% of your capital or a significant amount where one loss can wipe out most if not all of your capital.
Yes, both do have limited risk, but in a market with rising volatility, one would be less likely to lose the entire amount risked with a calendar spread than one would with a credit spread. Credit spreads are neg vega and positive theta; calendars are positive vega and positive theta.
Of course, a move of overwhelming size would turn either of the two into toast.