Tsumo (自摸, "self-draw") is a win completed with the tile a player draws from the wall on their own turn, as opposed to ron, which is claimed on an opponent's discard. The draw is the fourteenth effective tile in the structure; a declared kan adds a physical tile without adding a group slot. Every win is either tsumo or ron.
A tsumo win requires the hand to be in tenpai and to hold at least one yaku. When the hand is fully concealed (no chii, pon, or open kan), the self-draw itself grants the menzen tsumo yaku, worth one han, so a closed hand can win on tsumo with no other yaku. Outside pao liability, a non-dealer tsumo is paid by all three opponents, with the dealer paying double the non-dealer share; a dealer tsumo is paid equally by the three players.
Tsumo remains legal in furiten. On a standard four-group hand other than pinfu, it adds 2 fu; chiitoitsu stays fixed at 25 fu and yakuman ignore fu. On a closed hand, tsumo also adds menzen tsumo. A standard closed hand won by ron instead adds 10 fu. The exact payment depends on han, fu, dealer status, rounding, limit tiers and any pao liability.