Timed mating calculator
Found a plug? Get the date of each embryonic day (E-day) you need, and when the litter is due. Need embryos at a stage on a set day? See when to set up the pairs.
- Oct 19, 2026 nowPlug found (E0.5)
A plug shows mating, not pregnancy: confirm by weight gain or a visibly pregnant belly before relying on these dates.
- Oct 29, 2026 in 10 daysE10.5
10 days after the plug.
- Nov 2, 2026 in 14 daysE14.5
14 days after the plug.
- Nov 6, 2026 – Nov 8, 2026 in 18 daysBirth expected (E18.5–E20.5)
Most often E19.5. Check daily from the first date.
- Nov 27, 2026 – Nov 29, 2026 in 39 daysWean (P21)
Count from the actual birth date once the litter arrives.
Opens in Google Calendar, Outlook or Apple Calendar.
About these dates
Is the plug day E0.5, E0 or day 1?
It depends on who is counting. Most papers and The Jackson Laboratory call the morning a plug is found E0.5 (mating happened around midnight, half a day earlier). Some labs call it E0, and Charles River and some vendors call it gestation day 1. They describe the same embryos, one day or half a day apart, so say which one you use in methods and when ordering timed-pregnant mice.
Does a plug mean she is pregnant?
No. A plug shows that mating happened, not that it took. A good share of plugged females are not pregnant, so confirm by weight gain or a visibly pregnant belly before relying on the date, and set up more pairs than you need.
When are mouse pups born?
Usually 19 to 21 days after mating: E18.5 to E20.5 counting the plug day as E0.5, most often E19.5.
How do I get embryos at E14.5 on a given day?
Count back 14 days from that day to get the plug morning (E0.5), and put the females in with the male the evening before. Only females with a plug that morning will be at E14.5 on your day.
Common lab conventions, not veterinary advice. Your IACUC protocol and facility rules come first.
Litter already born? The wean date calculator gives the wean dates and when to take the male out.
How it’s worked out
Everything counts whole days from the morning the plug was found (day 0).
- Stage names: day d after the plug is Ed.5 (plug = E0.5), Ed (plug = E0) or GD(d + 1) (plug = gestation day 1).
- A stage's date: plug date + d days.
- Birth: plug date + 18 to 20 days (E18.5–E20.5), most often + 19.
- Wean: the birth window + 21 days.
- Planning back from a date: plug morning = your date − d days; set up pairs the evening before.
Example: a plug found on Monday, March 2 (E0.5) gives E14.5 on Monday, March 16, and birth expected March 20–22. To have E14.5 embryos on Thursday, April 16, set up pairs on the evening of Wednesday, April 1 and look for plugs on the morning of Thursday, April 2.
Sources
- The Jackson Laboratory: Timed pregnant mice
- The Jackson Laboratory: 6 steps for setting up timed pregnant mice
- Charles River: Timed pregnant mice and rats (plug day = day 1)
- Study of plug-positive C57BL/6J females that were not pregnant (PMC4521569)
Last checked against these sources on . Found a mistake? Tell us.