prices). The total amount of own resources that may be collected for the EU Budget from Member States in any given year is limited with reference to Member States' GNI. Currently, the total amount of own resources allocated to the Union to cover annual appropriations for payments cannot exceed 1.20% of the sum of all the Member States' GNI. The GNI for own resource purposes is calculated by National Statistical Institutes according to European law governing the sources and methods to compile GNI and the transmission of GNI data and related methodological information to the commission (Eurostat). Basic information must be provided by the countries concerned to Eurostat before 22 September in the year following the budget year concerned. Eurostat carries out information visits to the National Statistical Institutes forming part of the European Statistical System. Based on assessment reports by Eurostat, the Directorate-General for Budget of the Commission may notify to the Permanent Representative of the Member State concerned required corrections and improvements in the form of reservations on the Member State's GNI data. Payments are made monthly by Member States to the commission. Own resources payments are made monthly. Custom duties are made available by Member States after their collection. Payments of VAT- and GNI-based resources are based upon the budget estimates made for that year, subject to later correction. Other revenue Other revenue accounted for 12.4% of EU revenue in 2017. This includes tax and other deductions from EU staff remunerations, contributions from non-EU countries to certain programmes (e.g. relating to research), interest on late payments and fines, and other diverse items. As the balance from the previous year's budget is usually positive in comparison to the budget estimates, there is usually a surplus at the end of the year. This positive difference is returned to the Member States in the form of reduced contributions the following year. Own resources As per the 2021-2027 period a system of own resources will be introduced relying on levies collected by the EU. Correction mechanisms The EU budget has had a number of correction mechanisms designed to re-balance contributions by certain member states: The UK rebate, which reimbursed the UK by 66% of the difference between its contributions to the budget and the expenditures received by the UK. This rebate was not paid to the UK, but was rather deducted from the amount the UK was due to pay. The