Savings and investing guide
How to Calculate a Monthly Savings Contribution
To set a monthly savings amount, subtract money already reserved for the goal from the target and divide the gap across the months remaining. If you include interest, use a formula that matches deposit timing and rate assumptions. Start with a no-interest baseline so the plan does not rely on an uncertain return.
Start with the no-interest baseline
If the target is G, current goal savings are P, and there are n monthly deposits, the simple contribution is (G − P) ÷ n when G exceeds P. For a $5,000 goal, $800 already saved, and 14 months, the baseline is $300 per month. This assumes no withdrawals, fees, or price changes and does not depend on earning interest.
Include a constant monthly rate when appropriate
For equal end-of-month deposits and a constant monthly rate i, the future value of deposits is PMT × [((1+i)^n − 1) ÷ i]. The starting balance grows to P(1+i)^n. Solving for the deposit gives PMT = [G − P(1+i)^n] ÷ [((1+i)^n − 1) ÷ i]. If i is zero, use the no-interest division. Beginning-of-month deposits have one more period to earn interest.
A worked USD example
Suppose the target is $5,000, the starting balance is $800, the horizon is 14 months, and the assumed rate is 0.25% per month. With equal end-of-month deposits, the formula gives a contribution of about $293.16 per month. The exact result depends on the rate convention and deposit dates; a variable savings rate may change before the deadline.
Keep the deadline and goal realistic
If the monthly amount is too high, compare a later date, a different target, or planned one-time deposits. Separate the goal from emergency savings if using the same dollars twice would leave another need unfunded. Do not assume an uncertain investment return will close a shortfall on a fixed date.
Review progress rather than locking in the first estimate
Check the balance and remaining months periodically. Update for price changes, withdrawals, rate changes, and missed deposits. If you receive extra money, decide whether it belongs in this goal or another priority. A useful plan is one you can keep funding, and the estimate should make its assumptions visible. You can compare the actual balance with the planned balance after each deposit rather than waiting until the deadline. If progress is behind, recalculate using the remaining gap and remaining months; do not quietly assume a higher return will make up the difference.
Try the savings goal calculator
Enter the target, current savings, rate assumption, and timeline to estimate required contributions. The tool models the assumptions you enter; it does not guarantee the account rate, account fees, tax outcome, or final purchase cost. Compare the result with the no-interest baseline and your actual cash flow.
| Target | Already saved | Months | Monthly deposit |
|---|---|---|---|
| $5,000 | $800 | 14 | $300 |
Frequently asked questions
How do I calculate savings deposits with no interest?
Subtract the amount already saved for the goal from the target, then divide the gap by the number of planned deposits.
Should I include interest in a goal deadline?
You can model a rate scenario, but variable rates, fees, and deposit timing can change the result. Check the no-interest baseline too.
Sources and further reading
Try the calculator
Use the Savings Goal Calculator to explore your own numbers with the assumptions shown in the tool.
Related guides
Educational content only; not individualized financial, tax, or legal advice.