Colony Growth & Cage Planner

The calculator uses a straightforward deterministic model to estimate colony size and cage demand month by month. The core formula for animals weaned per month is:

weaned/month = breeding pairs × litter size × pre-weaning survival × (litters per year ÷ 12)

Each month, weaned animals are added to the standing (non-breeder) population. Monthly turnover is then applied as a fraction removed from that standing population — representing animals used in experiments, culled, or transferred out. If turnover is 0%, animals accumulate indefinitely; if it matches your weaning rate, the colony reaches a steady state.

Cage demand is calculated as the number of breeding pairs (one cage each) plus the ceiling of standing population divided by your animals-per-cage setting. This assumes breeders and non-breeders are housed separately, as is standard practice.

1. Enter your breeding setup — number of breeding pairs, typical litter size for your strain, and how many litters you expect per year (most mouse strains: 5–8).
2. Set pre-weaning survival — the percentage of pups you expect to survive to weaning. 90% is a good default for healthy inbred strains; lower this for strains with known perinatal issues.
3. Set monthly turnover — the fraction of your non-breeder population removed each month through experimental use, culling, or transfers. Match this to your actual usage rate to get a realistic steady-state estimate.
4. Set cage density — the number of non-breeder animals per housing cage allowed by your IACUC protocol or institutional guidelines (commonly 3–5 for mice).
5. Read the monthly table — the table shows weaned animals, standing population, total animals (including breeders), and total cages needed at each month. Use the 6- and 12-month snapshots for quick capacity planning.
6. Export or share — use the Export CSV button to download the full projection for your records or to paste into a budget spreadsheet, or copy the Share URL to send the same inputs to a colleague.