The number on your pay stub divided by 40 hours isn't your real hourly rate. It's the starting point before all the other costs.
Unpaid time — overtime, commuting, prep and decompression — means each dollar of take-home pay is actually spread over more hours than your contract says. Work expenses — commuting costs, work clothes, lunches — reduce what you actually keep. And taxes take a chunk before you see any of it.
Your true hourly rate is what you're trading each hour of your life for. It's the right number to use when deciding whether a raise is worth it, whether a commute is worth the salary difference, or whether going freelance or contracting makes financial sense.
Reducing work-related expenses directly increases it. So does remote work (eliminates commute time and cost). Unpaid overtime is the silent killer — an extra 10 hours/week effectively cuts your rate by 20%.