The formula
How to calculate time to save
The simplest version of the savings question, with interest deliberately left out: divide what is still missing by what you put aside each month. For anything inside a couple of years that is close enough to be the honest answer.
Leaving interest out is a feature here. On a two-year goal in a cash account, interest shortens the timeline by a few weeks at most — well inside the error on your own estimate of what you can save.
The calculator asks for:
- Amount needed
- Saved so far
- Saving each month
Results appear immediately — there is nothing to submit. Changing a field rewrites the link, so you can share the exact scenario you are looking at.
Worked example
Take the figures the calculator starts with:
- Amount needed: 12,000
- Saved so far: 2,500
- Saving each month: 400
That gives:
- Months needed: 23.8 months
- Years needed: 2 years
- Still to find: 9,500
Reading the result
Round the answer up, then add a month. Savings plans meet a car service, a vet bill or a wedding invitation, and the plans that survive are the ones with slack built in rather than the ones costed to the last pound.
Where this goes wrong. Assuming a monthly figure you have hit once. Use the average of the last three months of actual transfers, not the best of them.
Not for goals under three years or so — the difference is small and the assumption adds false precision. Beyond that, use a version that compounds, because growth starts to move the date meaningfully.
Use a conservative average and treat anything above it as pulling the date forward. Planning on the good months and hoping the lean ones do not arrive is how timelines slip.
The answer it gives you is months needed. With 12,000 amount needed, 2,500 saved so far and 400 saving each month, that comes to 23.8 months. Change any field and the figure moves with it.