# Exact formula ROBLOX uses to apply gravity to an object

Basically, I just need to know how gravity is applied, specifically the equation I can use to calculate a part’s position over time. I initially thought the equation was -(gravity / 2)x² + (starting Y velocity)x + (initial Y position). To test this, I applied Y velocity to a part and tried to predict what the vertex of its movement would be. However, the part always seems to come up a little bit short. For example, when applying a Y velocity of 100 to an object with standard gravity, the equation I came up with was -98.1x² + 100x. I expected the part to peak at roughly 25.484, but it actually peaked at roughly 25.268. Does anyone know what I’m missing here? If anyone could explain that, I would really appreciate it.

The devhub says it’s `Gravity/seconds^2` in studs per second.

I understand that, but can you explain why those slight deviations are occurring between my expected and actual vertexes? It looks like there’s some factor I’m missing.