Savings Goal Calculator
Enter your savings target, your current balance, your monthly deposit, and the interest rate to see how many months it will take to reach the goal — solved with the standard time-value-of-money formula.
Months to reach goal
41
- Years
- 3
- Extra months
- 5
- Final balance
- £10,107.73
- Total deposited
- £9,200.00
- Interest earned
- £907.73
Months to goal solves the future-value-of-annuity formula for n: n = ln((G + PMT/r) / (P + PMT/r)) / ln(1+r), where G is the goal, P is the starting balance, PMT is the monthly deposit, and r is the monthly rate (APR/12). With a 0% rate it reduces to (G − P) / PMT. Months are rounded up so the final balance equals or exceeds the goal.
How to use this calculator
Enter the savings goal you want to hit, your starting balance, how much you can add each month, and the annual interest rate the account pays. The calculator shows the number of months until you reach the target, broken down into whole years and remaining months, plus the final balance, total deposits, and interest earned along the way.
How the calculation works
It inverts the future-value-of-annuity formula. The future value after n months is FV = P · (1+r)^n + PMT · ((1+r)^n − 1) / r, where P is the starting balance, PMT is the monthly deposit, and r is the monthly rate (annual rate divided by 12). Rearranging for n gives n = ln((G + PMT/r) / (P + PMT/r)) / ln(1+r), where G is the goal. When the interest rate is zero, this simplifies to (G − P) / PMT. Months are rounded up so the final balance is at least equal to the goal — the same convention as Excel's NPER() function.
Worked example
Example: goal of $10,000, starting balance of $1,000, monthly deposit of $200, annual rate of 5% (monthly compounding). Monthly rate r = 0.05 / 12 ≈ 0.004167. PMT / r ≈ 48,000. Ratio = (10,000 + 48,000) / (1,000 + 48,000) = 58,000 / 49,000 ≈ 1.1837. n = ln(1.1837) / ln(1.004167) ≈ 0.16864 / 0.004158 ≈ 40.6 months. Rounded up, you reach the $10,000 goal in 41 months — three years and five months — having deposited $9,200 of your own money and earned roughly $800 in interest.
Frequently asked questions
How does a savings goal calculator work?
It works backwards from the future-value formula. Future value is what you get if you start with a known balance, add a regular deposit, earn a known rate, and let n months pass. A savings goal calculator already knows the future value (your target) and solves for n. The maths is one algebraic rearrangement of the future-value-of-annuity formula, the same identity behind Excel's NPER() and most retirement-planning tools.
What if my interest rate is 0%?
When the rate is zero, the maths collapses to simple division: months = (goal − starting balance) / monthly deposit. A goal of $5,000 with $0 starting and $250 per month takes 20 months at 0%. The calculator handles this case explicitly so you do not get a divide-by-zero result. If the rate is zero and the deposit is also zero, the goal is unreachable and the calculator says so.
Does this use simple interest or compound interest?
Compound interest, applied monthly. Each month the existing balance grows by one-twelfth of the annual rate, then the monthly deposit is added at the end of the month (an ordinary annuity). Over short horizons this is almost identical to simple interest; over long horizons the gap widens and compounding dominates. A 5% account compounded monthly produces an effective annual yield of about 5.12%, slightly higher than the headline rate.
How accurate is the result?
The formula is exact for the model — fixed monthly rate, fixed monthly deposit, end-of-month timing, no fees or withdrawals. Real accounts vary: rates change, providers credit interest at different intervals, and tax wrappers (ISAs, IRAs, 401(k)s) shelter growth that would otherwise be taxed. Treat the months-to-goal number as a planning target, not a contractual date. To be conservative, enter a slightly lower rate than the headline APY.
What if my goal is unreachable?
The calculator caps the search at 100 years and shows "Goal unreachable within 100 years" if the inputs cannot get there. The most common reason is a zero monthly deposit combined with a starting balance below the goal and no interest — in that case the balance never grows. Increase the monthly deposit, the rate, or both. A goal far above the starting balance with a small deposit is reachable in principle but may take decades, which is itself a useful signal.
Should I include inflation?
The result is nominal — the number of currency units at the future date, not adjusted for purchasing power. If you care about real (inflation-adjusted) buying power, subtract your expected inflation rate from the interest rate you enter. A 5% nominal rate with 2% inflation behaves like a 3% real rate, which lengthens the time to reach a fixed-currency goal noticeably.