The government has been paid at least ¥52 billion to borrow money since the yield on its debt first fell below zero at auction in October 2014.
While some of the bonds still pay coupons, prices on the securities are so high that the Ministry of Finance sells them for more than it costs to pay interest on the debt. Bloomberg calculations count money made on bills and notes that now have negative yields out to five-year maturities.
Japan follows Germany, Switzerland and Sweden in being able to get investors to pay it to raise funds, a windfall that will help Prime Minister Shinzo Abe tackle the world's largest debt burden. On the downside, Bank of Japan asset purchases and charges on some lenders' reserves have reduced bond-market activity and squeezed earnings for banks and their customers.