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Scope and Limitations

The system is designed to support specific tax calculations and it's important that you understand the scope and limitations of the system.

Browser requirements

ShareCalc runs inside your web browser rather than on our servers, so what your browser supports affects how you can use it.

  • A reasonably current browser with WebAssembly support is required. All major browsers released in the last few years qualify.
  • Storing your data in a file on your device requires the File System Access API. This is available in Chromium-based desktop browsers such as Chrome, Edge, Brave and Opera. Firefox, Safari and mobile browsers generally do not support it.
  • Where the File System Access API isn't available, ShareCalc detects this automatically and uses browser storage instead. Everything works the same way, but your data lives only in that browser on that device, and clearing your browsing data will delete it.
  • Whichever option you use, we hold no copy of your data and cannot recover it for you. See Getting Started.

Calculation scope

The system aim is to support accurate tax reports from the 2019/2020 tax year onwards. Transactions from prior years are supported only for the purposes of calculating correct section 104 holdings for use from 2019/2020 onwards. Reports are available for prior years for reference purposes, but the gains and income for those years may not be correct. For example, taper relief is not supported by the system.

The system currently has some further limitations:

  • Broker importers support specified export formats and recognised activity types, not every event a broker may record. Review skipped rows carefully. See Importing Data.
  • The system only supports calculations for individuals subject to income tax.
  • The system does not support clogged shares.
  • Calculations are only supported for dates from April 6, 1998
  • Offshore fund limitations:
    • Offshore funds are supported from December 1, 2009.
    • Funds that changed from reporting to non-reporting, or vice versa, are not supported
    • Automatic HMRC classification requires a valid ISIN for the exact share class. The absence of a reference-data match is not evidence that a fund is Non-Reporting; see Reference Data.
  • The system is in a beta testing phase and therefore the results may not be correct. In particular, the income calculations are in an early state of development.
  • The system does not account for the accrued income scheme small holdings exception. See SAIM4210.
  • The system generally validates that you own an asset when an interest or dividend payment arises from it, but this integrity check is not done for gilts.
  • UK REITs held before April 6, 2019 are not supported where the residency timeline includes any non-resident period. From that date non-resident disposals of UK REITs are chargeable and a REIT held on April 5, 2019 can be rebased to its market value on that date, which the system does not support. Where this applies the REIT asset will fail; UK REITs are fully supported for taxpayers who are resident throughout, and for holdings acquired on or after April 6, 2019.