When determining the cost of a spell, what should be factored in first?

When determining the cost of a spell in Magic: The Gathering, the first thing to be factored in is any additional costs and increases. This is because changes to the cost are made in a specific sequence as outlined in the Comprehensive Rules.

Initially, you will consider any additional costs that must be paid when casting the spell. These could be costs like paying extra mana, sacrificing a creature, or any other cost dictated by the spell's text or abilities that require payment. After additional costs are accounted for, any increases to the cost, whether from an opponent's effects or specific game mechanics, are considered.

Following the adjustments for additional costs and increases, the next step would be to apply any reductions or discounts that might apply. This clear order of operations ensures that all necessary factors affecting the spell’s total cost are properly assessed. Thus, focusing on additional costs and increases first lays the groundwork for calculating the final cost accurately.