In the survey, 35 participants claim to know their exact conception date. This is rare; most due dates are measured from last menstrual period because it's easier to track. But the general question that always comes up is "Would my due date be more accurate if based off the conception date?"
On the main probability chart I found that due dates have about an 8-10 day standard deviation, meaning that the bulk of the babies are dispersed within plus or minus 10 days of their due date.
For this graph, I subtracted each babies birth date from his or her conception date, then added 14 days across the board because that's usually what we do when calculating a due date based on conception.
The standard deviation didn't improve much when compared to all the women in the survey. So bad news... even if you know the second your baby was conceived, your due date won't be any more accurate.
There is a related chart that compares LMP due dates with ultrasound-determined due dates. It also found no noticable difference in standard deviation.
The statistics right now are as follows:
- Mean: 279 (39W,6D)
- Median: 278 (39W,5D)
- Standard Deviation: 9.51 days
- Most popular days to give birth:
- 278 (39W,5D) (5 births, 14%)
- 287 (41W,0D) (3 births, 9%)
- 283 (40W,3D) (3 births, 9%)
- 276 (39W,3D) (2 births, 6%)
- 272 (38W,6D) (2 births, 6%)
Data Table
The percentages are based on ALL births (including inductions)| Day | Week | Births | Running Total | Percent | Running Total % |
|---|---|---|---|---|---|
| 245 | 35W,0D | 0 | 0 | 0 % | 0 % |
| 246 | 35W,1D | 0 | 0 | 0 % | 0 % |
| 247 | 35W,2D | 0 | 0 | 0 % | 0 % |
| 248 | 35W,3D | 0 | 0 | 0 % | 0 % |
| 249 | 35W,4D | 0 | 0 | 0 % | 0 % |
| 250 | 35W,5D | 0 | 0 | 0 % | 0 % |
| 251 | 35W,6D | 0 | 0 | 0 % | 0 % |
| 252 | 36W,0D | 0 | 0 | 0 % | 0 % |
| 253 | 36W,1D | 0 | 0 | 0 % | 0 % |
| 254 | 36W,2D | 0 | 0 | 0 % | 0 % |
| 255 | 36W,3D | 0 | 0 | 0 % | 0 % |
| 256 | 36W,4D | 0 | 0 | 0 % | 0 % |
| 257 | 36W,5D | 0 | 0 | 0 % | 0 % |
| 258 | 36W,6D | 1 | 1 | 2.9 % | 2.9 % |
| 259 | 37W,0D | 0 | 1 | 0 % | 2.9 % |
| 260 | 37W,1D | 1 | 2 | 2.9 % | 5.7 % |
| 261 | 37W,2D | 0 | 2 | 0 % | 5.7 % |
| 262 | 37W,3D | 1 | 3 | 2.9 % | 8.6 % |
| 263 | 37W,4D | 0 | 3 | 0 % | 8.6 % |
| 264 | 37W,5D | 0 | 3 | 0 % | 8.6 % |
| 265 | 37W,6D | 1 | 4 | 2.9 % | 11.4 % |
| 266 | 38W,0D | 0 | 4 | 0 % | 11.4 % |
| 267 | 38W,1D | 0 | 4 | 0 % | 11.4 % |
| 268 | 38W,2D | 2 | 6 | 5.7 % | 17.1 % |
| 269 | 38W,3D | 0 | 6 | 0 % | 17.1 % |
| 270 | 38W,4D | 1 | 7 | 2.9 % | 20 % |
| 271 | 38W,5D | 1 | 8 | 2.9 % | 22.9 % |
| 272 | 38W,6D | 2 | 10 | 5.7 % | 28.6 % |
| 273 | 39W,0D | 0 | 10 | 0 % | 28.6 % |
| 274 | 39W,1D | 0 | 10 | 0 % | 28.6 % |
| 275 | 39W,2D | 0 | 10 | 0 % | 28.6 % |
| 276 | 39W,3D | 2 | 12 | 5.7 % | 34.3 % |
| 277 | 39W,4D | 1 | 13 | 2.9 % | 37.1 % |
| 278 | 39W,5D | 5 | 18 | 14.3 % | 51.4 % |
| 279 | 39W,6D | 0 | 18 | 0 % | 51.4 % |
| 280 | 40W,0D | 0 | 18 | 0 % | 51.4 % |
| 281 | 40W,1D | 1 | 19 | 2.9 % | 54.3 % |
| 282 | 40W,2D | 1 | 20 | 2.9 % | 57.1 % |
| 283 | 40W,3D | 3 | 23 | 8.6 % | 65.7 % |
| 284 | 40W,4D | 1 | 24 | 2.9 % | 68.6 % |
| 285 | 40W,5D | 0 | 24 | 0 % | 68.6 % |
| 286 | 40W,6D | 1 | 25 | 2.9 % | 71.4 % |
| 287 | 41W,0D | 3 | 28 | 8.6 % | 80 % |
| 288 | 41W,1D | 2 | 30 | 5.7 % | 85.7 % |
| 289 | 41W,2D | 2 | 32 | 5.7 % | 91.4 % |
| 290 | 41W,3D | 0 | 32 | 0 % | 91.4 % |
| 291 | 41W,4D | 0 | 32 | 0 % | 91.4 % |
| 292 | 41W,5D | 0 | 32 | 0 % | 91.4 % |
| 293 | 41W,6D | 1 | 33 | 2.9 % | 94.3 % |
| 294 | 42W,0D | 1 | 34 | 2.9 % | 97.1 % |
| 295 | 42W,1D | 1 | 35 | 2.9 % | 100 % |
| 296 | 42W,2D | 0 | 35 | 0 % | 100 % |
| 297 | 42W,3D | 0 | 35 | 0 % | 100 % |
| 298 | 42W,4D | 0 | 35 | 0 % | 100 % |
| 299 | 42W,5D | 0 | 35 | 0 % | 100 % |
| 300 | 42W,6D | 0 | 35 | 0 % | 100 % |