I need $50000 in 12 years. If I earn .25% per month how much do I deposit today?

Let's see if we can derive this formula.

The new month's balance would be Bal_1 = Bal_0*(1+i). The next month would do the same, giving a series of Bal_0*(1+i)*(1+i)

This reduces to Bal_n = Bal_0*(1+i)^n

Now you can solve for Bal_0 and substitute in the values for the original problem (being careful to treat months and percent properly).