The half marathon and the marathon look like close relatives, but their data behave differently. The half marathon is faster, more tactical early on and less affected by fuel and fatigue. The marathon rewards patience and has far more room for things to go wrong.
Comparing the two distances
In a half marathon, an athlete can often sustain a pace close to their limit for the whole race, so the splits tend to be flat and the gaps between runners are decided by small differences. In a marathon the same athlete must hold back early, and the second half usually shows more variation in pace. Doubling a half-marathon time does not predict the marathon time, because the demands are not the same.
Respecting the extra distance
Calculators that convert one distance to another are popular, and they can give a rough guide. They cannot know how the athlete handles fuel, heat or the last ten kilometres. A page like 20Bet Africa platform that lists results from both distances side by side is useful for seeing who is consistent, but the sensible reader treats any conversion as a loose estimate, not as a forecast.
A common calculator takes a half marathon time and predicts a marathon time. For an experienced athlete the estimate may be reasonable; for others it is often optimistic, because the marathon asks for fuel management, muscle endurance and mental stamina that the shorter race does not test.
Look at the second half of each. A runner who holds pace to the end of a half marathon has shown speed endurance; one who holds pace to the end of a marathon has shown something else. The two skills overlap without being the same, so a prediction is a guess, not a result.
It also helps to remember that equivalent-performance tables are built from averages. Individual runners differ: some are strongest over shorter distances, others over the full marathon. A table is a rule of thumb and should be read as such. Use it for a rough orientation before a race, and let the actual splits correct it.
If betting markets sit alongside half marathons and marathons on your screen, treat the budget as fixed before you begin. Agree a time limit with yourself, pause between sessions and walk away when the limit is reached; a bigger stake never makes a read more reliable.
The sensible way to finish is with modest expectations. Skill in comparing different race distances helps explain what happened; it does not remove the uncertainty that makes sport worth watching.