Find the monthly deposit that reaches a target, or how long a fixed deposit will take.
%
Enter the values to see the result here.
Formula
With monthly rate r (annual rate ÷ 12), n months, current savings S and target T:
D=(1+r)n−1(T−S(1+r)n)r
To find the time for a fixed deposit D instead, solve the same equation for n:
n=ln(1+r)ln(Sr+DTr+D)
The result is rounded up to whole months. When r=0 both formulas reduce to D=(T−S)/n and n=(T−S)/D.
Worked example
Target 50,000, nothing saved yet, 6% a year, 5 years.
r=0.005, n=60, (1.005)60≈1.34885.
D=50,000×0.005/(1.34885−1)≈716.64 per month.
You deposit 716.64×60≈42,998; the remaining 7,002 comes from returns.
With a 0% return the same goal needs 833.33 a month, so the 6% return saves about 117 every month.
Common mistakes
Using a high expected return to make the monthly figure look small. Plan with a conservative rate.
Forgetting existing savings, which also earn the return.
Entering years where months are expected in other tools. Here the time frame is in years and converted for you.
Ignoring inflation on a long goal, so the target buys less than planned.
Frequently asked questions
Should I include a return rate if I only keep cash?
Use 0 for cash under the mattress or a current account. A 0% rate makes the answer a plain division, which is the safest planning number for a short goal.
What does "monthly deposit needed" assume about timing?
Deposits happen at the end of each month and the annual rate is spread over 12 equal monthly rates. Your first deposit therefore earns 11 months of growth in a 12-month plan.
Why does the time-needed result say it will never be reached?
With a 0% return and a 0 deposit, or when interest on a falling balance cannot catch up, the balance never climbs to the target. Raise the deposit.
Is the target adjusted for inflation?
No. If the goal is a purchase in five years, add the expected price rise yourself, for example 3% a year, before entering the target.