It then asks the age and gender of each sexual partner.
When people list the age range of each partner, the calculator uses its database to work out, on average, how many previous sexual partners people within that age range have had.
It then repeats this process for five further 'generations' of partner. Added together, this provides a sex degrees of separation total.
For example, it shows that a 25-year-old man who has had nine female sexual partners has indirectly had sex with 485,051 people.
By contrast, a 45-year-old woman who has had ten male sexual partners has come into sexual contact with 6,324,624 people.
Finally, a 63-year-old man who has had 14 female sexual partners has indirectly had sex with 865,142 people.
The calculator helps to explain why sexually transmitted infection rates are on the rise at a time when the average man claims to have had nine sexual partners while the average woman admits to having had 6.3 lovers.
One reason why younger people may have higher scores than some older people is because of the increased number of sexual partner they have had.
Figures from the Health Protection Agency show that rates of sexually transmitted diseases are highest in young adults aged 15-24 years old, accounting for 57 per cent of all new gonorrhoea diagnoses and 56 per cent of all new genital warts diagnoses.
Cases of 'untreatable gonorrhoea' have soared by 25 per cent in a year, as experts warn the disease is becoming more resistant to treatment.
More than 20,000 new cases of the sexually-transmitted infection were diagnosed in 2011.
Furthermore, the number of gay men catching HIV has almost doubled in 20 years because new drugs have encouraged unsafe sex, research suggested.
Between 1990 and 2010, cases rose by 76 per cent due to fewer people using condoms. Experts say this is due to the introduction of antiretroviral drugs that are effective in treating the disease.
During this time there was a 26 per cent increase in the proportion having unprotected sex, according to the study.