I get a little giddy talking about this because Japanese handles 'I love you' like a whole palette of feelings rather than one blunt statement. In everyday speech the most common, flexible phrase is 好きだ (suki da) or the polite 好きです (suki desu). Both literally mean "I like you," but context does the heavy lifting: used in a confession between schoolkids or adults, 好きです often functions exactly like an English "I love you" without sounding dramatic. If you soften it — 好きかもしれない or ちょっと好き — it sounds tentative, which is great for nervous first confessions.
On the deeper end there's 愛してる (aishiteru) and the polite 愛しています (aishiteimasu). These carry a stronger, more committed connotation — think long-term devotion or marriage-level emotion. Japanese people often reserve 愛してる for very serious moments (dramas, wedding vows, or private, intense confessions). Outside that, you’ll see 大好き (daisuki) used a lot: it’s more emphatic than 好き but less formal than 愛してる, so it's cozy and affectionate. Then there are colloquialisms like 惚れてる (horeteru) meaning "I'm smitten/I've fallen for you," or 愛してるよ with a softer particle that feels intimate.
Formality shows up in verb endings and pronoun choices: 私はあなたを愛しています is unmistakably formal and serious, while 俺はお前が好きだ sounds rough and masculine. Couples rarely use あなた to each other; they use names or nicknames with -ちゃん/-くん. And a cultural note — words are often smaller actions are louder in Japan: many people express love through care, time, and small favors rather than grand verbal declarations. For anyone confessing, matching your words to the situation is the trick — a quiet 好きです at a school rooftop can mean everything, while 愛しています suits a quieter, solemn moment.