Is one month notice the same as four weeks?

Not always. One month follows calendar months while four weeks is always 28 days.

Is this legal advice?

No, this is a planning aid only.

Notice periods

Estimate one calendar month notice period end dates.

1 month notice period calculator UK: calculate the matching date in the next month.

One month notice can end on a different date from 4 weeks notice. Use the unit in your contract.

Is 1 month always 30 days?

No, it depends on the calendar month.

Should I use 4 weeks instead?

Only if your contract says four weeks, not one month.