a colloquial version (despite the Latin)

I take it that this has something to do with accounting, i.e. entries are made for items that will materialise at a later date (in the next return).

If this is the case, I would go for "expenditure in relation to which income will materialise in the following reporting period" (if it refers to the Vorleistungen made by the the reporting party to third parties) or "advances [income] in relation to which expenditure will materialise in the following reporting period" (if the Vorleistungen are made by third parties to the reporting party).

Other than that, I've also translated Vorleistungen as "preliminary work", "input", "previous work" and of course as suggested by Kim above.