Accountants and bankers have warned confusion about how to account for the 50% bonus tax is leading to uncertainty over how the banking sector will report its full year results. Senior bankers, accountants from the Big Four firms and regulators are among many who are struggling to understand the complexity issues surrounding the tax, particularly when knowing whether they should take a charge for the tax in 2009 or 2010, the Financial Times reports. Confusion stems from the government's announcement of the tax so close to the end of the year, the fact it is a one-off tax, and the flexibility of the international accounting standards that UK banks use when reporting. Banks that are still using US GAAP accounting rules are not required to provide for the tax until 2010, adding further confusion as some will be accounting for it in their 2009 report, causing concern over an 'uneven playing field'. Timing of the chancellor's bonus tax has also been dubbed a problem. Many banks will want to put aside funds to account for the tax, which although announced in December, will not become law until August. But under accounting rule IAS 37, the provisions for non-financial liabilities, companies are told not to provide for the impact of a tax on their balance sheets until it is guaranteed to become law.