I created this little website because I tend to leave things to the last minute, such as renewing an old website's certificate. There's nothing like a countdown timer to create a sense of urgency. I hope you find it useful.
It would be good if you could list several domains and show the countdown for whichever one is the next due to expire. Once that one gets renewed, shuffle the next one due into the countdown.
Or use lets-encrypt and automate renewals.
Thanks for the suggestion regarding multiple domains.
People should definitely use Let’s Encrypt. I certainly do where I can (e.g. ssltimer.com).