Naturally occurring platinum (₇₈Pt) consists of five stable isotopes (¹⁹²Pt, ¹⁹⁴Pt, ¹⁹⁵Pt, ¹⁹⁶Pt, ¹⁹⁸Pt) and one long-lived (half-life 4.83×10¹¹ years) radioisotope (¹⁹⁰Pt). There are also 34 known synthetic radioisotopes ranging from ¹⁶⁵Pt to ²⁰⁴Pt, and longest-lived of those is ¹⁹³Pt with a half-life of 50 years. All the others have half-lives under two weeks, most under a day. There are numerous metastable states, of which the most stable are ^193mPt and ^195mPt with half-lives 4.33 and 4.010 days, decaying to their ground states.

Despite the obstacles to measurement with rare isotopes of rare elements, with a very slow decay, the ¹⁹⁰Pt/¹⁸⁶Os system has been used in isotope geology, though not directly for dating.

All isotopes of platinum are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed. Platinum-195 is the most abundant isotope, making platinum one of the only three elements to have its most abundant isotope with an odd neutron number (the other two being beryllium and nitrogen); however, it is so only by a small margin, unlike the other two, and is more in the nature of a coincidence.

Daughter products other than platinum