It really depends on the period, country, area and what records might actually be available (church records, newspapers, family Bible, etc.).
Father-in-law's father was baptised 1 Jan.1864 (the date civil registration of births in Ireland started) so no birth certificate. Luckily his twin brother's daughter, then in her 90s, was alive, very lucid and able to verify the actual date the twins were born in December 1863.