When do you count missed period ?

Hi, so I’m a little worried because I realised I’m 6 days late for my period. When would you call it a missed period instead of a late period? I haven’t tested but I will do I think in maybe a day or two I’m just giving out hope it will turn up. I’ve only been with my man for two months and the thought of being pregnant scares me. I have no pregnancy symptoms though I feel the same as I always do. If the test is negative and there’s still not period when do you go doctors? I’m 24 and this has never happened to me so just want some advice 😊