The standard tax year in Luxembourg is the calendar year ending 31 December. Alternate tax years are possible with approval.
Annual tax returns must be filed no later than 31 May of the year following the calendar year in which the tax year ended. Extensions may be requested.
Effective 1 January 2021, companies liable for real estate levy should file a declaration (return), along with a certified report from an approved auditor, no later than 31 May following the calendar year in which the tax year ended. The first declaration is due on 31 May 2022 for the tax year 2021. Further, investment vehicles are required to declare whether or not real estate was held/owned in Luxembourg by 31 May 2022.
Companies in Luxembourg are required to make quarterly advance tax payments on 10 March, 10 June, 10 September, and 10 December. Each payment is set by the tax authorities and is usually equal to 1/4 of the tax liability of the previous year.
When taxable income is expected to vary substantially from the previous year, the advance payments may be adjusted accordingly. For new companies, the payments are estimated by the tax authorities.
Any outstanding balance due following the receipt of the final assessment should be paid within 1 month. If tax paid exceeds the final tax liability, the excess may be refunded.
Effective 1 January 2017, electronic filing of corporate tax returns has been made mandatory. ( https://guichet.public.lu/fr/entreprises.html)