Máy tính lợi nhuận trung bình
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Arithmetic vs. geometric averages
The arithmetic average simply adds the yearly returns and divides by the count. The geometric mean multiplies the growth factors and takes the n-th root — it answers "what constant return would have produced the same ending balance?". With +20% one year and −20% the next, the arithmetic average is 0%, but the account actually lost 4%, and the geometric mean reports −2.02%. Volatility drag makes the geometric mean the right number for planning.
Câu hỏi thường gặp
Which average should I use for projections?
Use the geometric mean. Compounding makes a sequence of returns multiply, not add, so only the geometric mean matches the growth of an actual account over the full period.
Why is my geometric mean so much lower?
Losses hurt more than gains help: a −50% year needs +100% to break even. The bigger the swings in your series, the larger the gap between the two averages.