By MoneyMaths · Calculation methodology
Start with three numbers: the target, the amount already saved and the time available. A return assumption can be added later. Starting with 0% makes it clear how much depends on your own contributions.
A goal without assumed growth
Suppose you want $20,000 and already have $2,000. You need another $18,000. Over 36 months that is $500 each month. Over 48 months it is $375 each month. Allowing one more year reduces the monthly commitment by $125.
| Plan at 0% return | Monthly saving | Time |
|---|---|---|
| Original deadline | $500 | 36 months |
| One extra year | $375 | 48 months |
| Save $300 per month | $300 | 60 months |
Make the shortfall visible
Saving $300 a month for three years adds $10,800. With the original $2,000, the total is $12,800 at 0% growth. The shortfall is $7,200. This does not mean saving $300 is pointless; it means the amount, target or deadline needs changing.
Use return assumptions carefully
A positive return can reduce the required deposit in a projection. It is not a promise that an account or investment will produce that return. The Investor.gov compound-interest calculator also separates starting money, contributions, time, interest assumptions and compounding frequency. MoneyMaths lets you compare nearby rate assumptions as well as a 0% savings-goal scenario.
For a fixed deadline, check what happens without growth. Taxes, fees, withdrawals and inflation are not included in these examples. If the goal is a future purchase, its price may change: update the target amount when you have a better estimate.
Build a plan you can maintain
- Choose a specific target amount and deadline.
- Enter the amount you can contribute after essential expenses.
- Read the projected shortfall or surplus.
- Compare an extra year and a 0% return.
- Save or print the assumptions and review them when circumstances change.
Original examples assume month-end deposits and no withdrawals. Updated 21 September 2026.