I'd say one every couple of years. https://letsencrypt.org/docs/certificates-for-localhost/ https://letsencrypt.org/docs/certificates-for-localhost/ has great

I'd say one every couple of years. https://letsencrypt.org/docs/certificates-for-localhost/ https://letsencrypt.org/docs/certificates-for-localhost/ has great documentation on that topic, including more examples.