Use this estimator for a transparent scenario based on an explicit base population and stated fertility, mortality, migration, or interpolation assumptions.

Mode

Component update after a census, or interpolation between two censuses.

Base population

Most recent census population (or earlier-census population in intercensal mode).

Births

Births registered since the base date (postcensal mode).

Deaths

Deaths registered since the base date (postcensal mode).

Net migration

Net migration since the base date; may be negative (postcensal mode).

End population

Later census population (intercensal mode only).

Fraction elapsed

Fraction of the interval elapsed from the earlier census (intercensal mode).

Estimate

Estimated population at the requested date.

A projection is conditional, not a prediction. Uncertainty increases with the horizon, and discontinuities in migration, boundaries, policy, fertility, or mortality can invalidate the assumed path.

Run multiple scenarios and compare them with a cohort-component projection when the necessary fertility, mortality, and migration schedules are available. Sensitivity ranges are more useful than a single extrapolated path.

• Census Date Midyear Conversion

  Convert a census count taken on an arbitrary date to a mid-year equivalent by exponential interpolation at an assumed constant annual growth rate over the elapsed days between the two dates.

• Headship Rate Household Projection

  Project the number of households with the headship-rate method: multiply each age group's adult population by its age-specific headship rate and sum across groups.

• School Age Population Projection

  Project a school-age cohort to the next planning date with the census survival ratio method: survivors equal the current cohort times l(x+n)/l(x), plus net school-age migrants.