They key difference:

• Farther is usually about physical distance.
• Further is about degree/amount or "more/in addition."

Example:

• We walked farther than yesterday. (more miles)
• We need to discuss this further. (more talk/ideas)

Read your sentence aloud.

• If you can touch or measure the distance, pick farther.
• If you can't measure it with a ruler, pick further.

Exceptions

Many speakers use further for both ideas and distance in casual speech.

Most style guides still prefer farther for distance and further for "more/extra".

Examples

• A2: The park is farther than the library.
• A2: We need further help to finish today.
• B1: After ten miles, we couldn't go any farther without water.
• B1: For further instructions, check your email.
• B2: The partnership will further the company's growth this year.
• B2: Before we hike farther, let's further our plan by checking the map.

FAQs

Q1: Can I use "further" for distance? Yes, in casual US/UK speech many do. But for clear writing, keep farther = distance, further = degree.

Q2: Is there a difference in pronunciation? No—both rhyme with "father." The difference is meaning and usage, not sound.

Q3: Which should I use in formal writing? Use farther for physical distance and further for degree/"more." Use further as an adjective (further details) and as a verb (further the project).