How long your cologne lasts depends on how you use it, the brand of cologne, the number of sprays you use, among other things. However, there are ways to get the best bang for your buck. You can aim for 4-5 sprays, ensuring the scent is not overpowering but lingers. Also, keep in mind that your skin's oil, sweat, and pH may affect how long your cologne lasts. On average, a 100ml bottle of cologne should last you around four to six months with moderate usage.