The short answer
A guppy is pregnant for about 28 days — roughly four weeks from mating to giving birth. The exact length shifts a little with temperature (warmer water tends to shorten it slightly), but 28 days is the reliable rule of thumb. At the end she delivers a batch of live, free-swimming fry, and thanks to stored sperm she can repeat the cycle several more times without mating again.
How the gestation works
After mating, the female carries the developing fry internally rather than laying eggs. Over the four weeks her belly grows rounder and then squarer, and the gravid spot near her vent darkens as the fry mature — late on you can sometimes see tiny eyes within it. A well-fed female in stable, warmish water (around 24–26°C) carries a healthy batch of anywhere from a dozen to fifty-plus fry. See our guppy care guide and how do I tell if my fish is pregnant.
Signs birth is near
As the 28 days close in, watch for:
- A very boxy, swollen abdomen.
- A large, dark gravid spot.
- Behaviour changes — hiding, hovering near the heater or substrate, going off food, and occasional contraction-like shivers.
After she gives birth
The fry are eaten within minutes in a community tank — including by their own mother — so have cover or a breeding box ready, and move her back once she’s done. Because she can deliver another batch in about 28 days, expect more fry soon. See how do I breed guppies, what do I do with baby fish, and what do I feed baby fish. Browse aquariums for a grow-out tank.