宝宝的出生日期，即预产期，可从准妈妈末次月经的第一天开始加280天（40周）来确定。只有50%的婴儿在预产期出生，预产期前两周或后两周内出生，都属于正常分娩。而怀孕未满37周分娩才称为早产，42周后分娩，称为过度妊娠。
利用下表可粗略计算出宝宝的出生日期。在左面一行找到末次月经的第一天，对应的右边一行日期就是宝宝的出生日期。例如，如果末次月经的第一天是2月5日，那么宝宝的出生日期约为11月12日（附表）。
| 1月 | 10月 | 2月 | 11月 | 3月 | 12月 | 4月 | 1月 | 5月 | 2月 | 6月 | 3月 | 7月 | 4月 | 8月 | 5月 | 9月 | 6月 | 10月 | 7月 | 11月 | 8月 | 12月 | 9月 |
| 1 | 8 | 1 | 8 | 1 | 6 | 1 | 6 | 1 | 6 | 1 | 8 | 1 | 7 | 1 | 8 | 1 | 8 | 1 | 8 | 1 | 8 | 1 | 7 |
| 2 | 9 | 2 | 9 | 2 | 7 | 2 | 7 | 2 | 7 | 2 | 9 | 2 | 8 | 2 | 9 | 2 | 9 | 2 | 9 | 2 | 9 | 2 | 8 |
| 3 | 10 | 3 | 10 | 3 | 8 | 3 | 8 | 3 | 8 | 3 | 10 | 3 | 9 | 3 | 10 | 3 | 10 | 3 | 10 | 3 | 10 | 3 | 9 |
| 4 | 11 | 4 | 11 | 4 | 9 | 4 | 9 | 4 | 9 | 4 | 11 | 4 | 10 | 4 | 11 | 4 | 11 | 4 | 11 | 4 | 11 | 4 | 10 |
| 5 | 12 | 5 | 12 | 5 | 10 | 5 | 10 | 5 | 10 | 5 | 12 | 5 | 11 | 5 | 12 | 5 | 12 | 5 | 12 | 5 | 12 | 5 | 11 |
| 6 | 13 | 6 | 13 | 6 | 11 | 6 | 11 | 6 | 11 | 6 | 13 | 6 | 12 | 6 | 13 | 6 | 13 | 6 | 13 | 6 | 13 | 6 | 12 |
| 7 | 14 | 7 | 14 | 7 | 12 | 7 | 12 | 7 | 12 | 7 | 14 | 7 | 13 | 7 | 14 | 7 | 14 | 7 | 14 | 7 | 14 | 7 | 13 |
| 8 | 15 | 8 | 15 | 8 | 13 | 8 | 13 | 8 | 13 | 8 | 15 | 8 | 14 | 8 | 15 | 8 | 15 | 8 | 15 | 8 | 15 | 8 | 14 |
| 9 | 16 | 9 | 16 | 9 | 14 | 9 | 14 | 9 | 14 | 9 | 16 | 9 | 15 | 9 | 16 | 9 | 16 | 9 | 16 | 9 | 16 | 9 | 15 |
| 10 | 17 | 10 | 17 | 10 | 15 | 10 | 15 | 10 | 15 | 10 | 17 | 10 | 16 | 10 | 17 | 10 | 17 | 10 | 17 | 10 | 17 | 10 | 16 |
| 11 | 18 | 11 | 18 | 11 | 16 | 11 | 16 | 11 | 16 | 11 | 18 | 11 | 17 | 11 | 18 | 11 | 18 | 11 | 18 | 11 | 18 | 11 | 17 |
| 12 | 19 | 12 | 19 | 12 | 17 | 12 | 17 | 12 | 17 | 12 | 19 | 12 | 18 | 12 | 19 | 12 | 19 | 12 | 19 | 12 | 19 | 12 | 18 |
| 13 | 20 | 13 | 20 | 13 | 18 | 13 | 18 | 13 | 18 | 13 | 20 | 13 | 19 | 13 | 20 | 13 | 20 | 13 | 20 | 13 | 20 | 13 | 19 |
| 14 | 21 | 14 | 21 | 14 | 19 | 14 | 19 | 14 | 19 | 14 | 21 | 14 | 20 | 14 | 21 | 14 | 21 | 14 | 21 | 14 | 21 | 14 | 20 |
| 15 | 22 | 15 | 22 | 15 | 20 | 15 | 20 | 15 | 20 | 15 | 22 | 15 | 21 | 15 | 22 | 15 | 22 | 15 | 22 | 15 | 22 | 15 | 21 |
| 16 | 23 | 16 | 23 | 16 | 21 | 16 | 21 | 16 | 21 | 16 | 23 | 16 | 22 | 16 | 23 | 16 | 23 | 16 | 23 | 16 | 23 | 16 | 22 |
| 17 | 24 | 17 | 24 | 17 | 22 | 17 | 22 | 17 | 22 | 17 | 24 | 17 | 23 | 17 | 24 | 17 | 24 | 17 | 24 | 17 | 24 | 17 | 23 |
| 18 | 25 | 18 | 25 | 18 | 23 | 18 | 23 | 18 | 23 | 18 | 25 | 18 | 24 | 18 | 25 | 18 | 25 | 18 | 25 | 18 | 25 | 18 | 24 |
| 19 | 26 | 19 | 26 | 19 | 24 | 19 | 24 | 19 | 24 | 19 | 26 | 19 | 25 | 19 | 26 | 19 | 26 | 19 | 26 | 19 | 26 | 19 | 25 |
| 20 | 27 | 20 | 27 | 20 | 25 | 20 | 25 | 20 | 25 | 20 | 27 | 20 | 26 | 20 | 27 | 20 | 27 | 20 | 27 | 20 | 27 | 20 | 26 |
| 21 | 28 | 21 | 28 | 21 | 26 | 21 | 26 | 21 | 26 | 21 | 28 | 21 | 27 | 21 | 28 | 21 | 28 | 21 | 28 | 21 | 28 | 21 | 27 |
| 22 | 29 | 22 | 29 | 22 | 27 | 22 | 27 | 22 | 27 | 22 | 29 | 22 | 28 | 22 | 29 | 22 | 29 | 22 | 29 | 22 | 29 | 22 | 28 |
| 23 | 30 | 23 | 30 | 23 | 28 | 23 | 28 | 23 | 28 | 23 | 30 | 23 | 29 | 23 | 30 | 23 | 30 | 23 | 30 | 23 | 30 | 23 | 29 |
| 24 | 31 | 24 | 1 | 24 | 29 | 24 | 29 | 24 | 1 | 24 | 31 | 24 | 30 | 24 | 31 | 24 | 1 | 24 | 31 | 24 | 31 | 24 | 30 |
| 25 | 1 | 25 | 2 | 25 | 30 | 25 | 30 | 25 | 2 | 25 | 1 | 25 | 1 | 25 | 1 | 25 | 2 | 25 | 1 | 25 | 1 | 25 | 1 |
| 26 | 2 | 26 | 3 | 26 | 31 | 26 | 31 | 26 | 3 | 26 | 2 | 26 | 2 | 26 | 2 | 26 | 3 | 26 | 2 | 26 | 2 | 26 | 2 |
| 27 | 3 | 27 | 4 | 27 | 1 | 27 | 1 | 27 | 4 | 27 | 3 | 27 | 3 | 27 | 3 | 27 | 4 | 27 | 3 | 27 | 3 | 27 | 3 |
| 28 | 4 | 28 | 5 | 28 | 2 | 28 | 2 | 28 | 5 | 28 | 4 | 28 | 4 | 28 | 4 | 28 | 5 | 28 | 4 | 28 | 4 | 28 | 4 |
| 29 | 5 | 29 | 3 | 29 | 3 | 29 | 6 | 29 | 5 | 29 | 5 | 29 | 5 | 29 | 6 | 29 | 5 | 29 | 5 | 29 | 5 | ||
| 30 | 6 | 30 | 4 | 30 | 4 | 30 | 7 | 30 | 6 | 30 | 6 | 30 | 6 | 30 | 7 | 30 | 6 | 30 | 6 | 30 | 6 | ||
| 31 | 7 | 31 | 5 | 31 | 8 | 31 | 7 | 31 | 7 | 31 | 7 | 31 | 7 |