Real Conditionals (αν + θα)
An open/real condition (“if X, then Y will happen”) uses αν (“if”) in the condition clause and θα in the result: Αν έχω χρόνο, θα γράψω (“If I have time, I will write”). The condition states something genuinely possible; the result is a θα-future. αν + present for the condition, θα + the perfective for the result is the everyday pattern.
The rule
A real (open) conditional - “if X, then Y will happen” - marks the if-clause with αν and the result with the θα-future: Αν έχω χρόνο, θα γράψω (“If I have time, I will write”). The everyday shape is αν + present in the condition and θα + the perfective in the result: Αν βρέχει, θα μείνω σπίτι (“If it rains, I’ll stay home”). This is only the real conditional; for the contrary-to-fact unreal ones (Module 10), the tense pair shifts - see Present-Unreal Conditionals and Past-Unreal Conditionals.