In most families the fixed shares fit the estate perfectly — they add up to exactly one. But not always. Sometimes the named fractions demand more than the whole estate, and sometimes they leave a surplus with no one obvious to take it. Two mechanisms resolve these, and both preserve fairness rather than breaking it.
ʿAwl — when the shares overshoot
Consider a woman survived by her husband and two full sisters. The husband's fixed share is one half; two full sisters together take two thirds. A half plus two thirds is more than a whole — the estate is over-subscribed.
The solution, agreed by all four Sunni schools, is ʿawl: the base of the problem is raised so the shares fit, and everyone is reduced in the same proportion. Here the base rises from six to seven, and the husband receives three sevenths while the sisters receive four sevenths. No one is dropped; each simply gives up a little.
Radd — when the shares fall short
The opposite case: a woman survived by her mother and one daughter. The mother takes a sixth and the daughter a half — together two thirds — and there is no son or other residuary heir to absorb the remaining third.
Rather than leave it undistributed, the surplus is returned (radd) to the fixed-share heirs in proportion to their shares. The mother and daughter end with a quarter and three quarters. One relative is excluded from the radd, however: a surviving spouse keeps their fixed share but does not share in the returned surplus.
The calculator applies both automatically and marks the result with an “ʿawl” or “radd” badge so you can see which was at work.