The idea of bail can be found in the Constitution. The Eighth Amendment to the Constitution says “Excessive bail shall not be required, nor excessive fines imposed, nor cruel and unusual punishments inflicted.” This, of course, means that the amount of bail required to be released from prison must match the severity of the crime. For non serious crimes, bail should be low. For serious crimes, such as murder, bail is set very high, and at times will not be allowed. The group that has the final say on what excessive bail might actually mean is the U.S. Supreme Court.
The purpose of bail is to release the criminal defendant from incarceration so he can assist in his criminal defense. A second reason is to decrease the population of jails. Bails are sureties, a guarantee that the defendant will return to the court at a later time to face the charges levied against him as outlined in the criminal complaint. In essence, when you bail someone out of jail, you are making a guarantee to the court that you will be responsible for their return when the court date arrives. Of course in some situations, bail is denied. The court makes this decision based on the severity of the alleged crime committed, the history of the defendant, and his ties to the community.
The amount of bail is calculated on a percentage of the bond. Depending on the jurisdiction, the bail ranges from 5-20 percent of the bond. It may be a cash bond or property bond. If the defendant fails to return for court or "skips bail" the person who signed the bond will forfeit that amount to the court.
In law bail is a security or assurance provided to a court of law for the release of an arrested person. The purpose of bail is to ensure that the person released on bail will reappear at the court to stand trial or be available for investigation of a crime if required.
The assurance in the bail can be in the form of money paid into the court, which is refunded when the person released on bail appears in court or is acquitted from the charges. In other cases the bail can be in the form of promise to pay money in case the person released on bail does not appear before court as required. This kind of promise is called bail bond. The amount of bail is decided by the court taking into consideration the seriousness of the alleged offence and the provisions of law for the same.
The bail may be granted after an arrest or at a trial. Sometimes a person who is sentenced by the court, but is allowed by the court to appeal may also be granted bail.
Bail may not be granted when it is feared that the person will not appear before the court as required, or the offence committed is very serious, or the person released on bail is likely to influence the witnesses or temper with other evidence.
Some countries also have a system of anticipatory bail. This system allows a person to apply for and get bail in relation to likely arrest in future for specified charges.