Interest is compounded monthly (annual rate ÷ 12) and each deposit is made at the end of the month. The first result counts months until your balance reaches the goal with your current monthly deposit. The second uses the annuity formula to find the deposit that reaches the goal exactly at your deadline.
Example: starting with 1,000 and saving 300 a month at 4% a year reaches 10,000 in about 29 months.
Subtract what you already have (grown by interest) from the goal, then spread the rest over the months left. With no interest it is simply (goal − saved) ÷ months; interest lowers the amount you need to put in.
No. Rates are treated as a fixed nominal return with no tax, fees or inflation. Use a lower rate to be conservative, or 0% to ignore interest.
See also: Compound Interest Calculator · Loan Calculator · Hourly to Salary