= 1 000 000 000 = milliard or so in many other languages.
If a decimal point automatically disappears whilst entering a value, then you should press
Ctrl+F to stop real-time updating, or first enter all digits and then the point at the right position.
P = billion
Maximum possible number of monogamous couples (all ages):
C = P/2 = billion
ESTIMATED number of regularly sexually active couples (initial estimate = C/2):
If each couple is active for 1 : of the time,
then 1 : of all couples are active at any moment.
So, if N, D, and F are accurate estimates:
couples world-wide are having sexual intercourse
World-wide births per week:
BW = per week = per minute
Births per activity:
S = BW/K = 1 :
Average female reproductive period:
= R×(365.25/7) = weeks
Number of activities in that time:
Y = RW×F =
Average total births per active woman:
Z = Y×S =
Note: C = P/2 = NW = total number of women and N = no. of active couples = no. of active women.
AF = N/NW = active fraction of women, so N = AF×NW,
and: RF = RW/LE = reproductive fraction of life time, so RW = RF×LE
(LE = female Life Expectancy, U.N. medium estimate for 2015-2020 = 74.29 years = 3876 weeks)
yields: Z = BW×RW/N = BW×(RF×LE)/(AF×NW) = BW×(RF/AF)×(LE/NW).
RF is the reproductive fraction of a life time, AF is the sexually active fraction of the population.
Ergodicity would mean RF = AF and the above initial values of N and R more or less reflect that.
It makes Z = BW×LE/NW.
Since BW×LE is the total number of births during a period of the same length as an average female life time,
this fertility number simply equals the number of births divided by the number of women.
Compare the above value of Z to the official U.N. values
taken from this Excel file.
Click in the date field or type Ctrl+D and enter any date in format:
"YYYY-MM-DD HH:NN:SS [Z|UTC|Z:±HHMM]",
then terminate input by typing Enter or clicking the Show button.
Trailing parts of a date+time may be omitted,
so for example "1957-11" translates to "1st of November, 1957, midnight".
Default date is the 1st of July of any year, time is interpreted according to the 24 hour system.
ANY substring of non-digits can be used as separator between numeric values.
The date part may also be specified as "DD-MON-YYYY", with "MON" being one of
"Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec" (or in Dutch: "Mrt,Mei,Okt").
If the input is terminated with "Z" or "UTC" it is interpreted as Coordinated Universal Time,
if it is terminated with a timezone prefixed with "Z:" (Z:±HH/Z:±MMM/Z:±HHMM) then that will be used,
else it is interpreted as Local Time according to your computer's timezone setting.
This page uses your computer's system time, assuming it is accurate.
Input can also be a count or number
prefixed with "C:" or "N:";
it will display the latest date on which the World Population was or will be equal to that amount.
Typing Ctrl+F or clicking the Freeze button stops real-time updating of the page (freezes it),
typing Ctrl+G or clicking the Real Time button starts real-time updating of the page.
As far as I can find out, data given by Worldometers are mainly based on U.N. data,
but Worldometers currently shows a lower number than the page you are reading right now.
This page uses data directly extracted from Excel sheets downloaded from the U.N. website.
As you can see above, the "official" milestone dates given by the U.N. are largely inconsistant with their own detailed data.
A probable cause is that accurate details became only available a few years after the milestone was proclaimed.
You can view the source code of this page (right-click on a non-active area of the page and find your way in the context menu),
This page uses Linear Interpolation between data points
(as well as linear extrapolation beyond 2100 for those who like to read tea-leaves).
I did not use any data from the U.S. Census Bureau, which presents lower numbers than the U.N. and Worldometers.
It is up to you to consider it either optimistic or pessimistic...