Final degree grade calculation for KCL

Does anyone know how to calculate what I would need to get in my third year to get a specific grade? Or what my final grade would be depending on what I get in my second and third years?

See Chapter 5, Progression and Award for Taught Programmes, in the King's Academic Manual - here.
In particular you want the Classification of Awards and General Award Rules sections, which are paragraphs 5.40 through 5.56.
Essentially what they say is that they take each module's mark (rounded to the nearest integer) and apply a weighted average across all your Year 2 and Year 3 modules. There are two weighting in effect: the number of credits in each module, and the year it was taken. (A module taken in Year 2 has a weighting of 2 and module taken in Year 3 has a weighting of 3, with Year 1 modules being ignored.) They then round the result to the nearest integer and apply the normal 70%, 60%, 50%, and 40% thresholds.
There are lots of other rules and caveats (particularly if you're close to a boundary), but that's the jist of it.

Hi, I would really want to find my c score before January, that's when I graduate. But are you sure about our module marks being rounded to the nearest integer? I thought that was done for the overall c-score and not individual marks. Please clarify, thank you so much.