The "Sex Degrees of Separation calculator" was developed by LloydsPharmacy Online and asks users to enter the number of men and women they have directly had sex with.
It then calculates the number of people they "indirectly" had sex with, based on that information.
On its website, LloydsPharmacy’s Online said the calculator was designed to highlight the risk of STIs.
"This calculator is not a diagnostic tool but it highlights how exposed you can be to STIs, and how this risk increases with each new partner," it said.
"It’s not just your direct partners that you have to worry about, but your partners’ partners, and their partners’ partners, and so on."
"Plus, even if you use condoms you are still exposed to several types of STI; including genital warts and herpes which can also be transferred through skin-to-skin contact, oral sex, and even sex toys.
"So the key message is to practice safe sex, but also to get regularly tested for STIs."
The calculator was released to coincide with Sexual Health Week in the UK.
