What this calculator does
Find out how much to save each month to reach your goal by the date you choose. A savings goal has three moving parts. There's the amount you want, the time you have, and how much your money grows along the way. You set the first two, and the calculator works out the monthly deposit that closes the gap.
Money you've already saved counts toward the target. It earns the same return as your new deposits. So a head start can shrink the monthly amount noticeably, or even remove it entirely.
Where it's used
Why this math matters outside the classroom:
- Monthly target. Reaching $10,000 in 3 years at 4% a year compounded monthly takes about $261.91 a month.
- Vacation fund. Families set a trip cost and a date and solve for the amount to set aside each month.
- Starting balance. Money already saved reduces the monthly deposit needed, because it grows toward the goal on its own.
- School supplies and tuition. Parents work out the monthly amount needed to reach a set sum by the first day of a school year.
Grade level and standards: Grades 11–12; Common Core State Standards for Mathematics HSA.SSE.B.4. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter your savings goal and the amount you've already saved toward it.
- Enter the yearly return you expect. Use 0 for a plain savings plan with no growth.
- Enter how many years you have. Part-years are fine: 1.5 years is 18 monthly deposits.
- Read the monthly deposit. You'll also see how much of the goal comes from your own deposits and how much from returns.
What the inputs mean
- Savings goal
- The total you want to have at the end, including what you already have. It must be above zero.
- Already saved
- Savings you've already set aside for this goal. Enter 0 if you're starting from nothing.
- Expected annual return
- The yearly return you expect. The calculator adds growth once a month (compounds it monthly). A savings account's advertised rate is a reasonable place to start. Investment returns aren't guaranteed.
- Time to reach goal
- The time until you need the money. It's turned into months and rounded to the nearest whole month, with a minimum of one month.
Formula and method
i = annual rate ÷ 100 ÷ 12 n = years × 12 (rounded to whole months) shortfall = goal − current × (1 + i)ⁿ deposit = shortfall × i ÷ ((1 + i)ⁿ − 1) deposit = shortfall ÷ n (when the rate is 0)
In the formulas, i is the monthly growth rate and n is the number of months. "Current" is what you've saved so far, and (1 + i)ⁿ means 1 + i multiplied by itself n times. First, the calculator grows the money you already have forward for n months. Whatever is still missing from the goal is the shortfall your new deposits need to cover.
The deposit formula works backward from a standard formula. That formula gives what equal deposits at the end of each month grow to over time. Here it's turned around to find the deposit instead. With a zero rate there's no growth, so the shortfall is split evenly across the months.
Your current savings may be on track to reach the goal by themselves. In that case, the deposit you need is zero, and the calculator shows the balance you can expect instead.
Worked example
You want $20,000 in 3 years, have $2,500 saved, and expect a 4% annual return.
- Monthly rate: 4 ÷ 100 ÷ 12 ≈ 0.003333, over 3 × 12 = 36 months.
- Growth factor: (1.003333)³⁶ ≈ 1.12727, so the $2,500 grows to about $2,818.18.
- Shortfall: 20,000 − 2,818.18 = 17,181.82.
- Deposit: 17,181.82 × 0.003333 ÷ (1.12727 − 1) ≈ $450.00.
Result: You need to save about $450.00 a month. Over 36 months that's about $16,200.11 in new deposits, with roughly $1,299.89 coming from returns.
Understanding the result
The monthly deposit is the least you can save and still reach the goal on time, if the return holds steady. Saving a little more gives you a cushion for months when returns fall short.
Compare the growth from returns with your total deposits. Over short periods, returns are a small share, and you reach the goal mostly by saving. Over long periods, growth on top of growth (compounding) does more of the work.
Assumptions and limitations
- You make deposits at the end of each month. Growth is added monthly, at a steady 1/12 of the yearly rate.
- The return stays the same the whole time. No taxes, fees or inflation are taken out.
- The goal is a fixed dollar amount. The calculator doesn't raise it to keep up with rising prices.
- Real investment returns change from year to year and can be negative. A fixed rate is a planning guess, not a forecast.
- It doesn't handle deposits that change over time, one-off extra deposits, or withdrawals before the goal date.
- Time is rounded to whole months, so 2.04 years and 2 years both give 24 deposits.
Frequently asked questions
Should I include inflation in the goal?
If the goal is a price that will rise, such as tuition or a car, yes. Estimate what it will cost when you need it and enter that figure. Or use a lower expected return, to roughly match growth after inflation.
What if I deposit at the start of each month instead?
Then each deposit earns one extra month of return. So the amount you need is slightly lower than shown: divide it by 1 + i, where i is the monthly rate. At 4% a year, that's about 0.33% less.
Why does the calculator say I need to deposit $0?
Your current savings, grown at the expected rate over your time frame, already meet or pass the goal. The calculator shows the expected balance, so you can see by how much.
What return should I use?
Use a rate that matches where the money will actually sit. For a short-term goal kept in a savings account, that account's rate makes sense. For money you must have on a fixed date, a cautious figure is safer than a hopeful one.
How this calculator is checked
Method: Future value of a lump sum plus future value of an ordinary annuity (end-of-period payments), solved for the payment. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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