The methanol to olefins process is an alternative for oil-based production of ethene and propene. However, detailed information on the reaction mechanisms of olefin formation in different zeolite is lacking. Herein a first principle kinetic study allows elucidating the importance of a side-chain mechanism during methanol conversion in H-SAPO-34. Starting from the experimentally observed hexamethylbenzene, a full low-barrier catalytic cycle for ethene and propene formation is found. The olefin elimination steps exhibit low free energy barriers due to a subtle interplay between an sp3 carbon center of the organic intermediate, stabilizing non-bonding interactions and assisting water molecules in the zeolite material.