I'm trying to figure out a world in my story (eg. whether dialects of a language would be mutually intelligible, how often would designer babies be born compared to 'usual' babies, usual family composition given lack of stigma towards single parents / same-sex couples) and the answers often come back related to time and population / population dynamics.
Essentially, I'd love it if there was a website where I could input stuff like...birth rate, death rate, initial population, average age at death etc and get some graphs so I could understand, for example, how many babies need to be born per year in order to sustain my population (initially I'm aiming for a population of 50 000 to 100 000, with a lifespan of 150 to 200 years, but I'd like to fiddle around with the parameters to see what I get).
Is there such a website you could recommend? (or Excel Sheet etc)