Usage note
“说不定”表示可能、也许，用来猜测不确定的事情。
“Shuō bú dìng” biǎoshì kěnéng, yěxǔ, yòng lái cāicè bù quèdìng de shìqíng.
"Shuō bú dìng" means maybe, perhaps, used to guess uncertain things.
Context note
当我们不确定一件事会不会发生时，可以用“说不定”。
Dāng wǒmen bù quèdìng yī jiàn shì huì bù huì fāshēng shí, kěyǐ yòng “shuō bú dìng”.
When we are not sure if something will happen, we can use "shuō bú dìng".
5 examples
说不定明天会下雨，记得带伞。
shuō bú dìng míng tiān huì xià yǔ， jì de dài sǎn。
Maybe it will rain tomorrow, remember to bring an umbrella.
说不定他能找到丢失的铅笔。
shuō bú dìng tā néng zhǎo dào diū shī de qiān bǐ。
Maybe he can find the lost pencil.
说不定老师会表扬我们。
shuō bú dìng lǎo shī huì biǎo yáng wǒ men。
Maybe the teacher will praise us.
说不定今天有体育课。
shuō bú dìng jīn tiān yǒu tǐ yù kè。
Maybe there is PE class today.
说不定她会来参加生日派对。
shuō bú dìng tā huì lái cān jiā shēng rì pài duì。
Maybe she will come to the birthday party.
5 mini stories
小明找不到他的橡皮，说不定在书包里。他翻了一下，果然找到了。
xiǎo míng zhǎo bú dào tā de xiàng pí， shuō bú dìng zài shū bāo lǐ。 tā fān le yí xià， guǒ rán zhǎo dào le。
Xiao Ming couldn't find his eraser, maybe it's in the backpack. He looked and found it indeed.
小红说，说不定明天会出太阳。她高兴地准备去公园玩。
xiǎo hóng shuō， shuō bú dìng míng tiān huì chū tài yáng。 tā gāo xìng dì zhǔn bèi qù gōng yuán wán。
Xiao Hong said maybe the sun will come out tomorrow. She happily prepared to go to the park.
小华想，说不定他能得到一个新玩具。他每天都很乖。
xiǎo huá xiǎng， shuō bú dìng tā néng dé dào yí gè xīn wán jù。 tā měi tiān dōu hěn guāi。
Xiao Hua thought maybe he could get a new toy. He is good every day.
妈妈对小明说，说不定今天有客人来。小明帮忙打扫房间。
mā mā duì xiǎo míng shuō， shuō bú dìng jīn tiān yǒu kè rén lái。 xiǎo míng bāng máng dǎ sǎo fáng jiān。
Mom said to Xiao Ming, maybe there will be guests today. Xiao Ming helped clean the room.
老师说，说不定这次考试很简单。同学们都松了一口气。
lǎo shī shuō， shuō bú dìng zhè cì kǎo shì hěn jiǎn dān。 tóng xué men dōu sōng le yì kǒu qì。
The teacher said maybe this exam is easy. The classmates all breathed a sigh of relief.
Mini dialogue
天气变化
A
明天说不定会下雨。
Míngtiān shuōbudìng huì xiàyǔ.
Maybe it will rain tomorrow.
B
那我们带伞吧。
Nà wǒmen dài sǎn ba.
Then let's bring an umbrella.
找东西
A
我的铅笔不见了。
Wǒ de qiānbǐ bújiàn le.
My pencil is missing.
B
说不定在书包里。
Shuōbudìng zài shūbāo lǐ.
Maybe it's in the schoolbag.
Related words and contrasts
similar
可能
kě néng
maybe; possible
可能 is more neutral for possibility; 说不定 implies a guess or uncertainty.
similar
也许
yě xǔ
perhaps; maybe
也许 is a common word for maybe; 说不定 is more colloquial and often used for sudden thoughts.
opposite
一定
yí dìng
definitely; certainly
一定 expresses certainty, the opposite of the uncertainty in 说不定.