Para calcular la significancia de un valor t, éste debe ser mayor que el del percentil correspondiente, dependiendo de si se trata de una prueba de una cola (unilateral) o de dos colas (bilateral)
Percentiles de la distribucion t de Student
| Prueba Unilateral | | | Prueba bilateral |
| Significancia | 0.05 | 0.01 | 0.001 | | | 0.05 | 0.01 | 0.001 |
| gl ⇓ | P95 | P99 | P99.9 | | | P97.5 | P99.5 | P99.95 |
| 4 | 2.1318 | 3.7469 | 7.1732 | | | 2.7764 | 4.6041 | 8.6103 |
| 5 | 2.0150 | 3.3649 | 5.8934 | | | 2.5706 | 4.0321 | 6.8688 |
| 6 | 1.9432 | 3.1427 | 5.2076 | | | 2.4469 | 3.7074 | 5.9588 |
| 7 | 1.8946 | 2.9980 | 4.7853 | | | 2.3646 | 3.4995 | 5.4079 |
| 8 | 1.8595 | 2.8965 | 4.5008 | | | 2.3060 | 3.3554 | 5.0413 |
| 9 | 1.8331 | 2.8214 | 4.2968 | | | 2.2622 | 3.2498 | 4.7809 |
| 10 | 1.8125 | 2.7638 | 4.1437 | | | 2.2281 | 3.1693 | 4.5869 |
| 11 | 1.7959 | 2.7181 | 4.0247 | | | 2.2010 | 3.1058 | 4.4370 |
| 12 | 1.7823 | 2.6810 | 3.9296 | | | 2.1788 | 3.0545 | 4.3178 |
| 13 | 1.7709 | 2.6503 | 3.8520 | | | 2.1604 | 3.0123 | 4.2208 |
| 14 | 1.7613 | 2.6245 | 3.7874 | | | 2.1448 | 2.9768 | 4.1405 |
| 15 | 1.7531 | 2.6025 | 3.7328 | | | 2.1314 | 2.9467 | 4.0728 |
| 16 | 1.7459 | 2.5835 | 3.6862 | | | 2.1199 | 2.9208 | 4.0150 |
| 17 | 1.7396 | 2.5669 | 3.6458 | | | 2.1098 | 2.8982 | 3.9651 |
| 18 | 1.7341 | 2.5524 | 3.6105 | | | 2.1009 | 2.8784 | 3.9216 |
| 19 | 1.7291 | 2.5395 | 3.5794 | | | 2.0930 | 2.8609 | 3.8834 |
| 20 | 1.7247 | 2.5280 | 3.5518 | | | 2.0860 | 2.8453 | 3.8495 |
| 21 | 1.7207 | 2.5176 | 3.5272 | | | 2.0796 | 2.8314 | 3.8193 |
| 22 | 1.7171 | 2.5083 | 3.5050 | | | 2.0739 | 2.8188 | 3.7921 |
| 23 | 1.7139 | 2.4999 | 3.4850 | | | 2.0687 | 2.8073 | 3.7676 |
| 24 | 1.7109 | 2.4922 | 3.4668 | | | 2.0639 | 2.7969 | 3.7454 |
| 25 | 1.7081 | 2.4851 | 3.4502 | | | 2.0595 | 2.7874 | 3.7251 |
| 26 | 1.7056 | 2.4786 | 3.4350 | | | 2.0555 | 2.7787 | 3.7066 |
| 27 | 1.7033 | 2.4727 | 3.4210 | | | 2.0518 | 2.7707 | 3.6896 |
| 28 | 1.7011 | 2.4671 | 3.4082 | | | 2.0484 | 2.7633 | 3.6739 |
| 29 | 1.6991 | 2.4620 | 3.3962 | | | 2.0452 | 2.7564 | 3.6594 |
| 30 | 1.6973 | 2.4573 | 3.3852 | | | 2.0423 | 2.7500 | 3.6460 |
| 35 | 1.6896 | 2.4377 | 3.3400 | | | 2.0301 | 2.7238 | 3.5911 |
| 40 | 1.6839 | 2.4233 | 3.3069 | | | 2.0211 | 2.7045 | 3.5510 |
| 45 | 1.6794 | 2.4121 | 3.2815 | | | 2.0141 | 2.6896 | 3.5203 |
| 50 | 1.6759 | 2.4033 | 3.2614 | | | 2.0086 | 2.6778 | 3.4960 |
| 60 | 1.6706 | 2.3901 | 3.2317 | | | 2.0003 | 2.6603 | 3.4602 |
| 70 | 1.6669 | 2.3808 | 3.2108 | | | 1.9944 | 2.6479 | 3.4350 |
| 80 | 1.6641 | 2.3739 | 3.1953 | | | 1.9901 | 2.6387 | 3.4163 |
| 90 | 1.6620 | 2.3685 | 3.1833 | | | 1.9867 | 2.6316 | 3.4019 |
| 100 | 1.6602 | 2.3642 | 3.1737 | | | 1.9840 | 2.6259 | 3.3905 |
| 300 | 1.6499 | 2.3388 | 3.1176 | | | 1.9679 | 2.5923 | 3.3233 |