Why work backwards from the goal?
Most people save whatever is left at the end of the month — and the amount is usually disappointing. Flipping the question to "how much do I need to put away each month?" turns a vague hope into a concrete, automatable number. Once you know the figure, you can set up an automatic transfer on payday and stop relying on willpower.
How the math works
The calculator first grows your existing savings forward: money you already have will compound until the deadline. Whatever gap remains must be covered by monthly deposits, and the required deposit is the annuity payment that future-values to that gap:
PMT = (Goal − P·(1+i)n) · i / ((1+i)n − 1)
where i is the monthly rate and n the number of months. If your current savings alone will out-grow the goal, the answer is simply zero.
A worked example
You want $30,000 for a house deposit in 5 years, already have $5,000, and your savings account pays 4%. Your $5,000 grows to about $6,100 on its own. The remaining $23,900 gap needs roughly $360 a month. Without any interest you would need about $415 a month — the account is quietly covering the difference.
Making the number stick
- Automate it. Schedule the transfer for the day after payday, so the goal is funded before spending starts.
- Revisit yearly. Rates change and goals drift. Re-run the calculation once a year and adjust.
- Keep goal money separate. A dedicated account reduces the temptation to raid it, and makes progress visible.