How to calculate a day rate
Day rate = hourly rate × hours in a working day. Most contractors use a 7.5- or 8-hour day. A weekly rate is the day rate × days per week, and a monthly rate uses about 4.33 weeks per month.
Why many freelancers prefer day rates
Clients compare day rates more easily, and you stop being judged on every 15 minutes. A day rate also protects you when a "two-hour" task quietly takes the whole day.