"Reverse FV" function? Or?

If you're looking for an alternative way to calculate the required monthly investment (not using PMT), you can also derive it using the future value of a series formula and solve it algebraically.

= (A2 - A4 * (1 + A3/12)^(A1*12)) / (((1 + A3/12)^(A1*12) - 1) / (A3/12))

This is mathematically identical to PMT, but avoids using built-in financial functions — useful if:

You want to understand what's happening behind the scenes.

You’re building a custom financial model.

You're using software without PMT.

...otherwise, for the sake of simplicity, I recommend the formula suggested by Mr. Vogelaar 🙂.