投資看周期，那是一定的。美國的經濟周期有規律嗎？下麵是美國自1857年以來的經濟周期表。
| Peak month(Peak Quarter) | Trough month (month Quarter) | Contraction | Expansion | Cycle | |
| Duration, peak to trough | Duration, trough to peak | Duration, trough to trough | Duration, peak to peak | ||
| December 1854 (1854Q4) | |||||
| June 1857 (1857Q2) | December 1858 (1858Q4) | 18 | 30 | 48 | |
| October 1860 (1860Q3) | June 1861 (1861Q3) | 8 | 22 | 30 | 40 |
| April 1865 (1865Q1) | December 1867 (1868Q1) | 32 | 46 | 78 | 54 |
| June 1869 (1869Q2) | December 1870 (1870Q4) | 18 | 18 | 36 | 50 |
| October 1873 (1873Q3) | March 1879 (1879Q1) | 65 | 34 | 99 | 52 |
| March 1882 (1882Q1) | May 1885 (1885Q2) | 38 | 36 | 74 | 101 |
| March 1887 (1887Q2) | April 1888 (1888Q1) | 13 | 22 | 35 | 60 |
| July 1890 (1890Q3) | May 1891 (1891Q2) | 10 | 27 | 37 | 40 |
| January 1893 (1893Q1) | June 1894 (1894Q2) | 17 | 20 | 37 | 30 |
| December 1895 (1895Q4) | June 1897 (1897Q2) | 18 | 18 | 36 | 35 |
| June 1899 (1899Q3) | December 1900 (1900Q4) | 18 | 24 | 42 | 42 |
| September 1902 (1902Q4) | August 1904 (1904Q3) | 23 | 21 | 44 | 39 |
| May 1907 (1907Q2) | June 1908 (1908Q2) | 13 | 33 | 46 | 56 |
| January 1910 (1910Q1) | January 1912 (1911Q4) | 24 | 19 | 43 | 32 |
| January 1913 (1913Q1) | December 1914 (1914Q4) | 23 | 12 | 35 | 36 |
| August 1918 (1918Q3) | March 1919 (1919Q1) | 7 | 44 | 51 | 67 |
| January 1920 (1920Q1) | July 1921 (1921Q3) | 18 | 10 | 28 | 17 |
| May 1923 (1923Q2) | July 1924 (1924Q3) | 14 | 22 | 36 | 40 |
| October 1926 (1926Q3) | November 1927 (1927Q4) | 13 | 27 | 40 | 41 |
| August 1929 (1929Q3) | March 1933 (1933Q1) | 43 | 21 | 64 | 34 |
| May 1937 (1937Q2) | June 1938 (1938Q2) | 13 | 50 | 63 | 93 |
| February 1945 (1945Q1) | October 1945 (1945Q4) | 8 | 80 | 88 | 93 |
| November 1948 (1948Q4) | October 1949 (1949Q4) | 11 | 37 | 48 | 45 |
| July 1953 (1953Q2) | May 1954 (1954Q2) | 10 | 45 | 55 | 56 |
| August 1957 (1957Q3) | April 1958 (1958Q2) | 8 | 39 | 47 | 49 |
| April 1960 (1960Q2) | February 1961 (1961Q1) | 10 | 24 | 34 | 32 |
| December 1969 (1969Q4) | November 1970 (1970Q4) | 11 | 106 | 117 | 116 |
| November 1973 (1973Q4) | March 1975 (1975Q1) | 16 | 36 | 52 | 47 |
| January 1980 (1980Q1) | July 1980 (1980Q3) | 6 | 58 | 64 | 74 |
| July 1981 (1981Q3) | November 1982 (1982Q4) | 16 | 12 | 28 | 18 |
| July 1990 (1990Q3) | March 1991 (1991Q1) | 8 | 92 | 100 | 108 |
| March 2001 (2001Q1) | November 2001 (2001Q4) | 8 | 120 | 128 | 128 |
| December 2007 (2007Q4) | June 2009 (2009Q2) | 18 | 73 | 91 | 81 |
| February 2020 (2019Q4) | 128 | 146 | |||
結論如下：
- 美國經濟有周期性；
- 周期的長短預測較困難；
- 周期的波峰和波穀及到達峰值的時間預測則更為困難；
