ほんとだ

That's true.

→ 本当
phrase Uncommon #18,336
That's true. Often said when realizing or agreeing that something is true. This is an informal form of 本当だ.
JA: えっ、ほんとだ!雨が降ってる。
EN: Oh, you're right! It's raining.

ほんとだあ!

It really is!

— かぐや姫の物語 (2013)

「ポップコーンの匂いがする」「ほんとだ!」

“It smells like popcorn.” “It really does!”

ほんとだ!

You're right!

— もののけ姫 (1997)

ほんとだね

That's true.

— JUNO/ジュノ (2007)

ほんとだ何だと思った?

Oh, you're right. What did you think it was?

— ダーク・プレイス (2015)

ほんとだよ

I really mean it.

— 七人の侍 (1954)

えっほんとだ!

Oh, you're right!

— すずめの戸締まり (2022)

ほんとだってば。

I'm telling you, it's true.

何を言ってるの?ほんとだ

What are you talking about? It's true.

— 動くな、死ね、甦れ! (1990)

いやほんとだよ

No, I mean it.

— 万引き家族 (2018)

ほんとだ

Oh, you're right.

— ザ・マン・フロム・アース (2007)

ほんとだねぇ

Yeah, that’s true.

— 魔女の宅急便 (1989)