Enter a rate in any period and see it in all the others at once. Because the conversion depends on how many hours and weeks you actually work, both are adjustable - which is what makes it possible to compare a contractor day rate with a salaried job honestly rather than by multiplying by 52 and hoping.
Multiply by hours per week and then by weeks worked per year. At 40 hours and 52 weeks, the shortcut is to double the hourly rate and add three zeros: 25 an hour is roughly 50,000 a year. The shortcut breaks down as soon as unpaid leave enters the picture.
Because unpaid time off, employer pension contributions, health cover, sick pay and gaps between contracts all come out of it. Setting working weeks to 46 or 44 rather than 52 shows the effect of that unpaid time; the rest has to be added on top as a margin.
Before. These are gross figures. Take-home pay depends on your country, region, filing status, pension contributions and allowances, none of which a general calculator can know.