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EARNINGS (LOSS) PER SHARE (EPS) - Diluted (Details) - BRL (R$) R$ / shares in Units, R$ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Allocated net income available to Common and Preferred shareholders |  |  |
Net income | R$ 2,365,763 | R$ 1,203,736 | R$ 2,303,868
Weighted - average number of shares outstanding |  |  |
Earnings per share - Diluted (Common and Preferred Shares) | R$ 1.38 | R$ 0.70 | R$ 1.34
Common shares |  |  |
Allocated net income available to Common and Preferred shareholders |  |  |
Net income | R$ 795,617 | R$ 405,607 | R$ 774,279
Adjustment to net income allocated to preferred shareholders in respect to the potential increase in number of preferred shares outstanding, as a result of long-term incentive plans of Gerdau. | (4,782) | (2,884) | (6,515)
Net income available to owners of parent including effects of dilutive shares | R$ 790,835 | R$ 402,723 | R$ 767,764
Weighted - average number of shares outstanding |  |  |
Weighted-average number of shares outstanding | 571,929,945 | 571,929,945 | 571,929,945
Preferred shares |  |  |
Allocated net income available to Common and Preferred shareholders |  |  |
Net income | R$ 1,570,146 | R$ 798,129 | R$ 1,529,589
Adjustment to net income allocated to preferred shareholders in respect to the potential increase in number of preferred shares outstanding, as a result of long-term incentive plans of Gerdau. | 5,524 | 2,884 | 6,515
Net income available to owners of parent including effects of dilutive shares | R$ 1,575,670 | R$ 801,013 | R$ 1,536,104
Weighted - average number of shares outstanding |  |  |
Weighted-average number of shares outstanding | 1,128,700,478 | 1,125,408,180 | 1,129,851,598
Potential increase in number of preferred shares outstanding in respect of long-term incentive plan of Gerdau | 10,821,083 | 12,157,614 | 14,440,860
Total | 1,139,521,561 | 1,137,565,794 | 1,144,292,458

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