What is the Savings Goal Time Calculator?
This calculator estimates how long it will take to reach a savings target — such as going from a small balance to $1,000,000 — when you contribute a fixed amount every month into an account that earns compound interest. It answers the practical question: "If I save $500 a month at 7% a year, how many months until I hit my goal?"
How to use it
Enter your savings goal (the future value you want to accumulate), your monthly contribution, and the expected annual interest rate. The calculator returns the number of years and months required, along with how much of the total comes from your own contributions versus compound interest growth.
The formula explained
The future value of an ordinary annuity is \( \text{FV} = \text{PMT} \times \left[ \dfrac{(1+r)^n - 1}{r} \right] \), where \(r\) is the monthly interest rate (annual rate \(\div\) 12) and \(n\) is the number of months. Solving for \(n\) gives:
$$n = \dfrac{\ln\left(\dfrac{\text{FV} \cdot r}{\text{PMT}} + 1\right)}{\ln(1 + r)}$$
If the interest rate is zero, the formula simplifies to \( n = \dfrac{\text{FV}}{\text{PMT}} \).
Worked example
Goal = $1,000,000, monthly contribution = $500, annual rate = 7%. The monthly rate \( r = 0.07/12 \approx 0.00583333 \). Then $$n = \dfrac{\ln\left(\dfrac{1{,}000{,}000 \times 0.00583333}{500} + 1\right)}{\ln(1.00583333)} = \dfrac{\ln(12.66667)}{\ln(1.00583333)} \approx \dfrac{2.539}{0.005817} \approx 436.57 \text{ months},$$ or about 36.4 years.
FAQ
Does this assume contributions at the start or end of the month? It uses an ordinary annuity (contributions at the end of each period), the standard convention.
Is interest compounded monthly? Yes — the annual rate is divided by 12 and applied each month.
Why is the answer a fraction of a month? The math yields a continuous value; in practice round up to the next whole month to be sure you reach the goal.
