Translation guide
The English verb "underestimate" can be expressed in Japanese through several verbs and phrases, depending on whether you mean misjudging a quantity, undervaluing a person or thing, or taking something too lightly. The most common and versatile word is 過小評価する, but in casual speech, 甘く見る or なめる are often used for people or situations.
Expressing that someone made an estimate or assessment that was too low, often leading to a mistake.
I underestimated his ability.
We ended up underestimating the cost of the project.
To look down on someone's ability or worth; to underestimate a person. Often used when the person proves you wrong.
I underestimated him. He's actually amazing.
Literally 'to look sweetly', meaning to not take something seriously enough, to underestimate a challenge or opponent. Common in casual speech.
I underestimated the exam. I should have studied more.
If you underestimate your opponent, you'll get hurt.
Very casual, often rude. Means to make light of someone or something, to not take seriously. Can imply contempt.
Can sound aggressive or confrontational. Use only in very informal situations.
Is that guy underestimating me?
Expressing that someone fails to recognize how good, important, or influential something is.
Again the standard formal term, works for value and importance as well.
The importance of this invention is underestimated.
To make light of, to disregard as unimportant. Often used for abstract things like risks, opinions, or warnings.
He underestimates the importance of his health.
To despise or look down on, often leading to underestimation. Slightly literary or formal.
Specifically about numerical estimates, like time, cost, or size.
過小評価する is the safest, most neutral choice for any kind of underestimation. 甘く見る is common in everyday speech when you fail to take a challenge seriously. なめる is very casual and can be offensive; it implies looking down on someone with contempt.
I underestimated his true ability. (neutral)
I didn't take the test seriously enough. (casual)
That new guy, I underestimated him (looked down on him) and he got amazing results.
なめる is slang and can be very rude. Avoid using it with superiors or in formal situations. Stick to 過小評価する or 甘く見る unless you are with close friends.
Never underestimate your opponent.
I underestimated how long it would take.
Casual
You must not underestimate that warning.
敵を侮ってはいけない。
Don't underestimate the enemy.
I underestimated the time needed.