Colony Population Calculator

Three-Scenario TNVR Impact Projector

Colony Parameters

Total cats in colony

Number already neutered

Projection period 10 years

Three-Scenario Population Projection

Never managed (no TNVR ever)

TNVR stopped (no new efforts)

Actively managed (ongoing TNVR)

— Never managed

— TNVR stopped

— Actively managed

🐾 Even when that last cat won't be caught — every neutered cat in a managed colony matters. Ongoing TNVR is the only scenario where the colony humanely declines over time.

About this tool
This calculator is intended as an educational tool to help illustrate the impact of Trap-Neuter-Vaccinate-Return (TNVR) on community cat populations. Results are projections based on research-backed assumptions and are meant to be informative, not precise predictions. Actual colony outcomes will vary based on many real-world factors including food availability, territory, immigration of new cats, local predators, disease, and the consistency of TNVR efforts.

Key assumptions used in this model
• 50% of unaltered cats are assumed to be female
• Unaltered females produce an average of 2–3 litters per year with ~4 kittens per litter
• Approximately 25% of kittens survive to breeding age (6 months)
• Kittens can begin reproducing at 6 months old
• Age-based mortality rates are applied separately to neutered and intact cats
• Neutered cats live significantly longer than intact cats (median ~10 years vs ~4 years) based on published research
• The "Actively Managed" scenario assumes new kittens are TNR'd at the same rate as the existing colony
• The "TNVR Stopped" scenario assumes no new cats are neutered after the starting point
• The "Never Managed" scenario assumes the colony was never altered

Sources
Mortality and lifespan data are based on peer-reviewed studies of managed feral cat colonies, including research from the University of Florida and University of New South Wales. Kitten survival rates reflect published field observations from TNR programs.

This tool was developed by Bailey's Human Rescue to support TNVR education across Johnston, Harnett, and Wake Counties, NC. We Rescue Humans, One Animal at a Time.