The formula for fixed contributions
If initial capital is P, the fixed monthly contribution is C, the monthly rate is r and there are n months, future value with end-of-month contributions is:
FVend = P × (1 + r)n + C × ((1 + r)n − 1) ÷ rFor start-of-month contributions, every contribution receives one extra growth period:
FVstart = P × (1 + r)n + C × ((1 + r)n − 1) ÷ r × (1 + r)- P
- initial capital
- C
- fixed monthly contribution
- r
- equivalent monthly rate
- n
- total number of months
With monthly compounding and nominal annual return i, r = i ÷ 12. Cifra Clara also supports other compounding frequencies and converts their effective growth into an equivalent monthly rate before simulating cash flows.
Contribute at the start or end of the month
The engine adds a start-of-month contribution before monthly growth and an end-of-month contribution afterwards. The early difference is small, but it compounds across 240 months.
Cifra Clara’s default scenario
The table below uses neither a historical nor a forecast return. It applies these visible, constant assumptions exactly as the calculator does on first load:
- Initial capital
- €10,000
- Monthly contribution
- €300
- Nominal return
- 6 % a year
- Compounding
- Monthly
- Contribution increase
- 2 % a year
- Timing
- End of month
- Hypothetical inflation
- 2 %
- Estimated tax
- 19 % on gains
Because the contribution increases by 2% at the start of each annual block, the closed formula explains the mechanism but the table is produced month by month. Tax is estimated as one charge on positive gains if the whole balance were liquidated at each annual snapshot; it is not an actual tax calculation.
Reproducible annual table
| Year | Contributed | Gross capital | Estimated net | Real value |
|---|---|---|---|---|
| 0 | €10,000.00 | €10,000.00 | €10,000.00 | €10,000.00 |
| 1 | €13,600.00 | €14,317.45 | €14,181.13 | €13,903.07 |
| 2 | €17,272.00 | €18,975.20 | €18,651.59 | €17,927.33 |
| 3 | €21,017.44 | €23,995.72 | €23,429.85 | €22,078.47 |
| 4 | €24,837.79 | €29,402.90 | €28,535.53 | €26,362.42 |
| 5 | €28,734.54 | €35,222.13 | €33,989.49 | €30,785.33 |
| 6 | €32,709.24 | €41,480.40 | €39,813.88 | €35,353.58 |
| 7 | €36,763.42 | €48,206.37 | €46,032.21 | €40,073.81 |
| 8 | €40,898.69 | €55,430.54 | €52,669.49 | €44,952.90 |
| 9 | €45,116.66 | €63,185.30 | €59,752.26 | €49,998.01 |
| 10 | €49,419.00 | €71,505.07 | €67,308.71 | €55,216.59 |
| 11 | €53,807.38 | €80,426.44 | €75,368.82 | €60,616.35 |
| 12 | €58,283.52 | €89,988.28 | €83,964.38 | €66,205.34 |
| 13 | €62,849.19 | €100,231.91 | €93,129.19 | €71,991.89 |
| 14 | €67,506.18 | €111,201.20 | €102,899.15 | €77,984.69 |
| 15 | €72,256.30 | €122,942.80 | €113,312.37 | €84,192.76 |
| 16 | €77,101.43 | €135,506.26 | €124,409.34 | €90,625.46 |
| 17 | €82,043.46 | €148,944.21 | €136,233.07 | €97,292.56 |
| 18 | €87,084.32 | €163,312.59 | €148,829.22 | €104,204.18 |
| 19 | €92,226.01 | €178,670.82 | €162,246.31 | €111,370.86 |
| 20 | €97,470.53 | €195,082.02 | €176,535.84 | €118,803.56 |
| Final | €97,470.53 | €195,082.02 | €176,535.84 | €118,803.56 |
After 20 years, total contributions would be €97,470.53. Simulated gross gain would be €97,611.49; estimated net capital €176,535.84; and purchasing power, with constant 2% inflation, €118,803.56 in today’s euros.
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Official source, interpretation and limits
The CNMV framework includes understanding compound returns, inflation, the risk-return relationship and regular long-term investing. This simulation does not model volatility, fees, interim losses, tax bands or changing returns and inflation.
The 6% rate is a constant mathematical assumption, not a promise or market forecast. Investments can rise or fall and real outcomes may differ substantially.