Annual pay is hourly wage × hours per week × weeks per year. To go the other way, divide the annual salary by the hours worked in a year (hours per week × weeks per year). Monthly pay is the annual figure divided by 12. Amounts are gross, before tax and deductions.
At 40 hours a week for 52 weeks, $25 an hour is $52,000 a year, about $4,333 a month.
Divide the yearly salary by 2,080, which is 40 hours × 52 weeks. For example, $60,000 ÷ 2,080 = $28.85 an hour.
If you take unpaid time off, lower the weeks worked per year (for example 50) to see what you actually earn. Paid holidays and vacation count as worked weeks.
See also: Hours Calculator · Percent Change Calculator · Sales Tax Calculator