Tinker 
How to use the savings goal calculator
Type the amount you want to end up with, how much you have already put aside, and the number of months until you need the money. Add the annual interest rate your savings account pays, or 0 if the money will not earn interest.
The main result is the deposit to make at the end of each month. You also see a weekly equivalent (the monthly figure times 12, divided by 52), the total of your new deposits, and how much of the goal is covered by interest.
The formula
The monthly rate r is the annual rate divided by 12 and by 100. Money you already have grows to Current × (1 + r)^n after n months. Subtract that from the goal to get the amount your deposits must build.
Regular monthly deposits made at the end of each month grow to Payment × ((1 + r)^n − 1) ÷ r. Rearranging gives Payment = Remaining × r ÷ ((1 + r)^n − 1). With no interest it is simply Remaining ÷ n. If your current savings alone will reach the goal, the required deposit is zero.
Worked example
Say you want $10,000 in 12 months, start from nothing, and your account pays 6% a year. The monthly rate is 0.5%, and 1.005^12 = 1.06168. The deposit is 10,000 × 0.005 ÷ 0.06168 = $810.66 per month, or about $187.08 a week.
Over the year you deposit $9,727.97 and interest supplies the remaining $272.03. With the default values (goal $20,000, $2,000 saved, 36 months, 4%), you need about $465 a month, deposit roughly $16,732 in total, and earn around $1,268 in interest.
Tips for hitting your goal
Results assume a fixed interest rate and deposits on the same day every month, so treat them as an estimate. Real savings rates change, and interest may be taxed, so consider rounding your deposit up a little.
Set up an automatic transfer on payday so the money moves before you can spend it. If the monthly figure is too high, try stretching the timeline by a few months or lowering the goal and see how much the payment drops.
Frequently asked questions
How much do I need to save each month to reach $10,000 in a year?
With no interest, $10,000 ÷ 12 = $833.33 a month. At 6% annual interest compounded monthly, about $810.66 a month is enough because interest adds roughly $272.
Does interest make a big difference?
For short goals, not much. Over several years it matters more: the longer the money sits, the larger the share of the goal that interest covers.
Should I save weekly or monthly?
Either works. Saving weekly spreads the effort and can earn slightly more interest since money goes in sooner. The weekly figure shown is the monthly deposit times 12 divided by 52.
What if I already have enough saved?
If your current savings, plus any interest, reach the goal by the deadline, the calculator shows a required deposit of zero and your projected ending balance.