就算 / 就是……也……: even if (spoken)
【六52】复句 / complex sentences (让步)
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
就算 / 就是 + hypothesis, (subject) + 也 + result: this is the "even if" of everyday conversation. You set up a case, often an extreme one, and say the result stays the same. The second half carries 也 (or 还是), never 但是.
The hypothesis can be an unlikely case (就算你变成大胖子), a limit pushed with 再 (就是再忙，他也会回家看看), or even a fact you grant in order to go beyond it (就算他错了，你也不能当着大家的面说他). Before a noun it takes the sense of "even": 就算成绩最好的同学，也答不出这道题.
就算 and 就是 are the colloquial counterpart of 即使 (hsk3-g33, hsk4-g02) and of the more written 即便 / 纵然 (hsk6-g03). Don't confuse them with 虽然……但是……, which states a real fact ("although"), whereas 就算 supposes or concedes ("even if"). Register: spoken and everyday written.
Examples
就算下雨，我们也要去。
Jiùsuàn xià yǔ, wǒmen yě yào qù.Even if it rains, we're going.
就算你不说，我也知道是谁干的。
Jiùsuàn nǐ bù shuō, wǒ yě zhīdào shì shéi gàn de.Even if you don't say anything, I know who did it.
就是再忙，他也会回家看看。
Jiùshì zài máng, tā yě huì huí jiā kànkan.However busy he is, he'll still go home for a visit.
就算他错了，你也不能当着大家的面说他。
Jiùsuàn tā cuò le, nǐ yě bù néng dāngzhe dàjiā de miàn shuō tā.Even if he is wrong, you can't tell him so in front of everyone.
就算成绩最好的同学，也答不出这道题。
Jiùsuàn chéngjì zuì hǎo de tóngxué, yě dá bu chū zhè dào tí.Even the best student couldn't answer this question.
就是请十个人来帮忙，一天也搬不完这么多书。
Jiùshì qǐng shí ge rén lái bāngmáng, yì tiān yě bān bu wán zhème duō shū.Even with ten people helping, you couldn't move this many books in a day.
Common mistakes
✗ 就算他错了，你就不能说他 → ✓ 就算他错了，你也不能说他 (the main clause carries 也 or 还是, not 就: 就 would mean "then", as in 如果……就……).
✗ 就算天气不好，但是我们也去 → ✓ 就算天气不好，我们也去 (no 但是: it belongs to 虽然……但是……).
✗ 就算下雨，我去 → ✓ 就算下雨，我也去 / 我还是去 (you need 也 or 还是 to get the "all the same").