What if…
Pull the paper. Each year is printed on the roll; the slider and the table say the same thing.
Start from an example
- A smaller surplus and a short term.
- The default example: 600 a month for ten years.
- Scenario B adds 200 a month and one point of interest.
Drag the paper, or use the slider. Left and right arrows move one month; Page Up and Page Down move a year.
- Put in
- €74,000
- Interest
- €8,074
- Balance
- €82,074
Scenario A
Your result
- Money you put in
- €74,000
- Interest earned
- €8,074
- Set aside each month
- €600
- Share of income saved
- 21%
- Goal reached
- 2 years 6 months
- Balance after 10 years
- €82,074
Balance by year (the roll as a table)
| Year | Put in | Interest | Balance |
|---|---|---|---|
| 0 | €2,000 | €0 | €2,000 |
| 1 | €9,200 | €107 | €9,307 |
| 2 | €16,400 | €361 | €16,761 |
| 3 | €23,600 | €766 | €24,366 |
| 4 | €30,800 | €1,324 | €32,124 |
| 5 | €38,000 | €2,039 | €40,039 |
| 6 | €45,200 | €2,913 | €48,113 |
| 7 | €52,400 | €3,951 | €56,351 |
| 8 | €59,600 | €5,154 | €64,754 |
| 9 | €66,800 | €6,528 | €73,328 |
| 10 | €74,000 | €8,074 | €82,074 |
Year 0 is today. Deposits are made at the end of each month.
In plain words
If you set aside €600 a month and earn 2.0% a year, you would have €82,074 after 10 years. Of that, €74,000 is money you put in and €8,074 is interest.
You would reach €20,000 in 2 years 6 months.
What changed
Move a slider to see what changes and why.
Nothing you enter is sent or stored. Calculations run in your browser.
The formulas
These are the exact formulas the calculator uses. Nothing is hidden.
- Set aside each month
- c = max(0, income − spending)
- If spending is at or above income, c is 0.
- Monthly rate
- r = yearly rate ÷ 100 ÷ 12
- A yearly rate of 2.0% gives r = 0.001667.
- Balance after n months
- B(n) = start × (1 + r)^n + c × ((1 + r)^n − 1) ÷ r
- When r is 0: B(n) = start + c × n. Deposits are made at the end of each month.
- Money you put in
- start + c × n
- Interest earned
- B(n) − (start + c × n)
- Months to a goal
- n = ceil( ln( (goal × r + c) ÷ (start × r + c) ) ÷ ln(1 + r) )
- When r is 0: n = ceil((goal − start) ÷ c). Zero if start is already at or above the goal. Not reached if it takes more than 600 months.
Worked example
Start 2,000. Income 2,800, spending 2,200, so c = 600. Rate 2.0%, so r = 0.02 ÷ 12 = 0.0016667. After 10 years, n = 120: (1 + r)^120 = 1.22039. B = 2,000 × 1.22039 + 600 × (1.22039 − 1) ÷ 0.0016667 = 2,440.78 + 79,633.42 = 82,074.20. Money put in: 2,000 + 600 × 120 = 74,000. Interest: 82,074.20 − 74,000 = 8,074.20.
Now: €82,074.20 after 10 years with these settings.
What this does not include
- Tax on interest, fees, inflation or changes in the rate.
- Changes in income or spending over time.
- Deposits at any time other than the end of each month.
- Any real product. The rate is yours to choose, and it is an example, not an offer.