It is because you have to use the "kun-yomi" 訓読み rather than the "on-yomi" 音読み for this kanji in this particular context. Most kanji in Japanese have at least two pronunciations (sometimes more!) - one is the Japanese pronunciation for words of Japanese origin, and there is also one (or more) pronunciation for those words of Chinese origin. Here, 度 is a word of Japanese origin, so you have to pronounce it using the kun-yomi, so tabi is the right pronunciation. On the other hand, if you say 毎度, then you use the Chinese pronunciation まいど。 This is a quick rule of thumb (because there are always exceptions): in most cases, if a kanji is used alone (rather than in groups of two or more), it is probably of Japanese origin, and you'll have to use the kun-yomi. For example: これは、私の物（もの）です。(Japanese pronunciation of the kanji 物） それは、動物（どうぶつ）です。(Chinese pronunciation of the same kanji) Of course, as I noted, there are always exceptions: 物語 is pronounced ものがたりbecause even those it has two kanji, 物語 is a compound word of Japanese origin, so you use the Japanese pronunciation. I hope this was helpful.

I will give you some examples. 一度 - ひとたび once (this is also often read as 'いちど') 二度 - ふたたび twice (this is also read as 'にど' ; another way of writing this is '再び') 三度 - みたび three times (this is also often read as 'さんど') Likewise, you can say 四度(よたび), 五度(いつたび), and so on. 幾度 - いくたび (how) many times 度々 - たびたび often この度 - this time …する度に - every time you do something/whenever something happens ※ 叔父は会う度に小遣いをくれる My uncle gives me allowance every time we see each other. As Brian mentioned this is a word of Japanese origin, so actually it is more recommendable to write it in hiragana.