Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes) and the mass defect of the nucleon binding is always small compared to the nucleon mass, the atomic mass of any atom, when expressed in daltons (making a quantity called the "relative isotopic mass"), is within 1% of the whole number A.
sˈɪns pɹˈoʊtɑːnz ænd nˈuːtɹɑːnz hæv ɐpɹˈɑːksɪmətli ðə sˈeɪm mˈæs ænd ðə mˈæs ʌvðɪ ᵻlˈɛktɹɑːnz ɪz nˈɛɡlɪdʒəbəl fɔːɹ mˈɛni pˈɜːpəsᵻz ænd ðə mˈæs dˈiːfɛkt ʌvðə nˈuːklɪən bˈaɪndɪŋ ɪz ˈɔːlweɪz smˈɔːl kəmpˈɛɹd tə ðə nˈuːklɪən mˈæs, ðɪ ɐtˈɑːmɪk mˈæs ʌv ˌɛni ˈæɾəm, wˌɛn ɛkspɹˈɛst ɪn dˈɔltənz mˌeɪkɪŋ ɐ kwˈɔntᵻɾi kˈɔːld ðə "ɹˈɛlətˌɪv ˌaɪsətˈɑːpɪk mˈæs", ɪz wɪðˌɪn wˈʌn pɚsˈɛnt ʌvðə hˈoʊl nˈʌmbɚɹ ˈeɪ.