Investing calculators
The saving-and-investing math for people with irregular income: steady contributions, honest assumptions, and every formula on the page. Projections use a constant assumed return; markets do not work like that, and each tool says so.
Tools in this section
- 001 Dollar-cost averaging calculator A fixed monthly contribution, compounded: invested vs growth.
- 002 Crypto gains calculator (FIFO) Realized gain across your buys and sells, oldest lots first.
- 003 Position size calculator How much to buy so a stopped-out trade costs what you chose.
- 004 Wash sale calculator Which of your harvested losses the 61-day window disallows.
Guides in this section
- Declaring Revolut in Spain: what still applies Revolut's Spanish branch issues ES IBANs, so the account is no longer foreign. What still applies: tax on interest and gains, plus forms 720 and 721.
- Declaring Trade Republic in Spain: check your IBAN first Trade Republic's Spanish branch issues ES IBANs, and the DGT confirmed those accounts are exempt from forms 720 and 721. What changes and what does not.
- 1099-B, 1099-DA and Form 8949: reporting investment sales Broker sale to tax return: what the 1099-B and new 1099-DA report, how lots land on Form 8949, and where Schedule D totals it.
- How to check a US broker before opening an account The free official lookups: FINRA BrokerCheck for brokers, the SEC adviser search, investor.gov for both, and the red flags the regulators list.
- How to check if a platform is authorised in Spain The three CNMV steps before any money moves: search the official registers, cross-check the warnings list, and spot the boiler-room signals.
- Crypto taxes in Spain: rates and form 721 Selling, swapping and staking are taxed in the savings base at 19-30%; form 721 reports foreign-custodied crypto over 50,000 euros, paying nothing.
- Foreign brokers from Spain: which obligations trigger Using a foreign broker from Spain changes who does the work, not the tax: no Spanish withholding, form 720 above 50,000, treaty dividends, no more D-6.
- The wash sale rule: the 61-day window that eats losses Sell at a loss, rebuy within 30 days either side, and the loss defers into the new basis. How the window works and why direct crypto stays exempt in 2026.