I do my best to hide major spoilers to any content related to episodes of Doctor Who later than the one a given page is about. These spoilers can be shown by clicking/tapping on them or selecting their text.
Every spoiler is marked by the series number. If you read a post about an episode from some series, and there is a spoiler warning about that very series, it means that it may spoil you some later episode.
There is one caveat about the specials. I assign specials to series somewhat randomly – for example, spoilers for The Christmas invasion is counted with Series 2 (that is, the following one), but spoilers for 2008-2010 specials are counted with Series 4 (that is, the preceding one). That makes sense, however, because while most specials take place after the series finale, the David Tennant specials are sort of extended finale for Series 4.
Also, since many people start watching New Who with series 5, if/when I get to series 5, I plan to mark spoilers to series 1–4 there, too. But please, do yourself a favor and do not watch series 5 past episode 3 if you haven’t watched series 1–4. You’ll thank me later;-).