Conservative4 % a year
€142,004
estimated net capitalCompound interest calculator
Calculate savings growth with monthly contributions, inflation and estimated tax. Compare three scenarios, free and without signing up.
Interactive calculator
Build your scenario
Adjust the assumptions and compare future value before tax, after tax and in today's money.
Result after 20 years
€176,536
estimated net capital
- Gross final capital
- €195,082
- Total contributed
- €97,471
- Accumulated gain
- €97,611
- Estimated tax
- −€18,546
- Real purchasing power
- €118,804 net capital expressed in today's euros
Effective annual rate: 6.17%Contribution: end of month
Private calculation. Your figures are processed on this device and are not sent to a server.
Simulation, not a forecast. It assumes a constant return, constant inflation and one tax rate. It excludes fees, interim losses and regulatory changes and is not financial or tax advice.
Range of outcomes
Three scenarios, one strategy
We compare the base assumption with annual returns two percentage points lower and higher.
Base6 % a year
€176,536
estimated net capitalOptimistic8 % a year
€223,662
estimated net capitalAnnual evolution
How the capital grows
GrossNetContributed
| Year | Gross capital | Total contributed | Gain | Estimated tax | Net capital | Real value |
|---|---|---|---|---|---|---|
| Today | €10,000 | €10,000 | €0 | €0 | €10,000 | €10,000 |
| 1 | €14,317 | €13,600 | €717 | €136 | €14,181 | €13,903 |
| 2 | €18,975 | €17,272 | €1,703 | €324 | €18,652 | €17,927 |
| 3 | €23,996 | €21,017 | €2,978 | €566 | €23,430 | €22,078 |
| 4 | €29,403 | €24,838 | €4,565 | €867 | €28,536 | €26,362 |
| 5 | €35,222 | €28,735 | €6,488 | €1,233 | €33,989 | €30,785 |
| 6 | €41,480 | €32,709 | €8,771 | €1,667 | €39,814 | €35,354 |
| 7 | €48,206 | €36,763 | €11,443 | €2,174 | €46,032 | €40,074 |
| 8 | €55,431 | €40,899 | €14,532 | €2,761 | €52,669 | €44,953 |
| 9 | €63,185 | €45,117 | €18,069 | €3,433 | €59,752 | €49,998 |
| 10 | €71,505 | €49,419 | €22,086 | €4,196 | €67,309 | €55,217 |
| 11 | €80,426 | €53,807 | €26,619 | €5,058 | €75,369 | €60,616 |
| 12 | €89,988 | €58,284 | €31,705 | €6,024 | €83,964 | €66,205 |
| 13 | €100,232 | €62,849 | €37,383 | €7,103 | €93,129 | €71,992 |
| 14 | €111,201 | €67,506 | €43,695 | €8,302 | €102,899 | €77,985 |
| 15 | €122,943 | €72,256 | €50,686 | €9,630 | €113,312 | €84,193 |
| 16 | €135,506 | €77,101 | €58,405 | €11,097 | €124,409 | €90,625 |
| 17 | €148,944 | €82,043 | €66,901 | €12,711 | €136,233 | €97,293 |
| 18 | €163,313 | €87,084 | €76,228 | €14,483 | €148,829 | €104,204 |
| 19 | €178,671 | €92,226 | €86,445 | €16,425 | €162,246 | €111,371 |
| 20 | €195,082 | €97,471 | €97,611 | €18,546 | €176,536 | €118,804 |
Transparent methodology
What this does and does not calculate
The simulation compounds the selected return and adds contributions every month. Net value subtracts a single tax rate from positive gains as if the full investment were liquidated; real value discounts accumulated inflation.
Real outcomes may include volatility, fees, tax bands and changing inflation. Check any decision against official information and seek professional advice where appropriate.
Read the CNMV guide on inflation and savingHow to calculate compound interest with monthly contributions
Example: €10,000 initially and €100 per month for 10 years
Simulated gross final balance: €31,998.32
Hypothetical 5% nominal annual return, monthly compounding and month-end contributions. No inflation, tax or contribution increases. Total contributed: €22,000. This is not a return promise.
Frequently asked questions
What is compound interest?
Interest is added to the balance and participates in subsequent periods' calculations. This simulation applies a constant rate; a real investment can fluctuate and lose value.
How do I include monthly contributions?
Enter your starting balance, monthly contribution and number of years. Choose beginning- or end-of-month contributions and an optional annual increase. With a positive rate, beginning-of-month contributions have more time to compound.
What is the difference between gross, net and real capital?
Gross capital includes simulated growth. Net capital deducts the tax percentage you enter from positive gains at the end of the term. Real capital adjusts the net amount for your inflation assumption. This is a simplification, not personalised tax advice.
Can I simulate no contributions or a negative return?
Yes: set monthly contributions to zero if you have an initial balance, or start from zero and contribute each month. Negative rates are supported within the input limits. The calculator neither guarantees gains nor predicts markets.
Finanzas para Todos: simple and compound interest (Spanish) ↗
An Artis Habitat S.L. tool · Educational estimates, not financial advice. Editorial standard, privacy and corrections contact.
DECISION GUIDES
P6Compound interest with monthly contributionsReproducible case and table→