GDP is calculated as the total of the current quarter and the three previous quarters. For any quarter(s) that GDP has not yet been published, the most recently-published GDP statistics are used. Sources: Bank of England, Federal Reserve, Macrobond and the Riksbank  Figure 12. Government bonds, municipal bonds, mortgage bonds and corporate bonds over time Nominal amounts, SEK billion 7 000 6 000 5 000 4 000 3 000 2 000 1 000 0  13  14  15  16  17  18  Central government  MFI, covered  Municipality and Kommuninvest  Non-financial corporations  19  20  Note. Securities debt in different sectors. MFIs (monetary financial institutions) include banks, mortgage institutions and finance companies. The series for municipalities’ securities debt refers to individual municipalities’ and regions’ borrowing and the borrowing through Kommuninvest i Sverige AB. The statistics refer to securities debt in SEK and foreign currencies. Sources: Statistics Sweden and the Riksbank  34 [35]  Figure 13. Central banks’ government bond purchases in relation to GDP in Sweden, the euro area, USA, UK and Japan Per cent of GDP 100 80 60 40 20 0  The Riksbank  ECB  Federal Reserve  Bank of England  Bank of Japan  Note. Nominal holdings as of 31 March 2021. Striped bars represent the Riksbank’s purchases of municipal bonds. Sources: Macrobond and national central banks  Figure 14.
One question that many nevertheless ask in the light of today's relatively large balance sheets, is whether we should expect them to be large in the future. 44 There are many indications that this is the case. A short-term policy rate will always be an important monetary policy tool, but my assessment is that bond purchases will play a bigger role than before. As I said, the balance sheet is very large at present. This means that even if we wanted to reduce it rapidly, it would take a long time before it is back at the levels that applied prior to the global financial crisis 2008-2009. But there are also a number of economic reasons why the central banks’ balance sheets should be large going forward. 45  General low level of interest rates in Sweden and abroad If interest rates continue to be as low as now, the policy rate will hit the lower bound more often. Monetary policy will thus automatically become more dependent on other instruments to be able to affect interest rates and access to credit. Extensive asset purchases will thereby become a more important instrument, but other measures, such as forward guidance, and interventions on the foreign exchange market, could also become relevant. The Riksbank has already been using a form of forward guidance since 2007, in that we have published a policy rate path.