The maxim of  equity regards as done what should have been done refers to the situation where the individuals are by an agreement or by law supposed to perform an act, equity will consider the parties to be in the position where they would have been had the obligations under the contract were fulfilled.

This maxim works in favour of the party or parties who were entitled to that performance. To understand this doctrine we first need to understand the concept of equitable conversion, which arises out of the doctrine of equity that equity regards that as done which ought to have been done.

In the English case of Fletcher v. Ashburner equitable conversion was defined as:
That change in the nature of property by which, for certain purposes, real estate is considered as personal, and personal estate as real, and transmissible and descendible as such.

To make this legal concept of equitable possible the maxim of equity regards as done what should have been done comes into play.

Origin
The origin of equity lies in the common law which evolved based on morality, natural justice and conscience. It started with the intervention of the crown in rendering justice when the king was extraordinarily asked to deliver justice utilizing a petition. Such cases were referred to Lord Chancellor who heard cases and passed judgments solely on grounds of natural justice and notion of conscience.

This practice of addressing the chancery (chancellor's office) became common and gave birth to the court of chancery and it created a new law which is now known as the law of Equity. The decisions were highly personal so the decisions were personal ideas of right and wrong of chancellor and non-compliance resulted in imprisonment. The Judicature Act of 1873 fused equity with Common Law. Gradually the concept of Equity, Justice and Good conscience became an in severable part of many legal systems across the globe and as a result, we have the doctrines of equity which are as follows:

1. Those that come to equity must come with clean hands;
2. Those who seek equity must do equity;
3. Equity regards as done that which ought to be done;
4. Equity follows the law; and
5. Delay defeats equity

Meaning And Application

Let's understand the meaning of this maxim with help of an example, Annie and Maya entered into a contract where Maya was supposed to do something in favour of Annie but she failed to perform the entire contract and completed only a part of her obligations so in this situation equity will regard Annie and Maya to be in the position where they would have been had Maya fulfilled here obligations entirely.

This maxim is applicable in situations where the defendant is bound in equity to perform any obligation and it considers the consequences which would have occurred had the original contract been performed. So basically when someone is obligated for the other courts of equity look at it as done and give the same results as if obligations had been performed actually.

The application of the maxim can be seen in the concept of executory contracts, part performance and the most common application is the doctrine of conversion.

Seaton v. Slade court said:
The effect of a contract for purchase is very different at Law and in Equity. At Law the estate remains the estate of the vendor; and the money that of the vendee. It is not so here. The estate from the sealing of the contract is the real property of the vendee. It descends to his heirs. It is divisible by his will; and the question, whose it is, is not to be discussed merely between the vendor and vendee; but may be to be discussed between the representatives of the vendee.

So one of the most important applications of this maxim is the concept of equitable conversion as discussed above.

For instance A gifted a property to B but before actual registration of the deed B died in such situations the questions as to if the property would descend to B's heirs if he died intestate, or was it personal estate, or should it devolve upon his administrators? Would it go to the spouse of the deceased? If the purchase money, when paid, belong to the heirs or to the administrators of the vendor? All the questions of this kind was resolved by the doctrine of equitable conversion as it is used to make a buyer the equitable owner of title to the property at the time that they sign a contract binding them to purchase the land at a later date.

The buyer is deemed the equitable owner after the contract is signed but before the closing. Just like in this example B has become the equitable owner of the property after the contract is signed but the deed has not been conveyed yet. In the case of Rockland Company v. Leary Judge Vann said in part in discussing this subject:
The doctrine of equitable conversion rests on the presumed intention of the owner of the property and the maxim that equity regards as done what ought to be done. The conversion usually becomes effective at the date of the instrument expressing it, if a deed or contract, and if a will, at the date of the testator's death.

Equity will never let a defendant enrich himself at the plaintiff's expense by depriving the plaintiff of equitable rights, so the equity court applies the maxim of equity looks on that as done which ought to have been done and focuses on the consequences of the performance of the contract. It looks at the situation or position where the parties would have been had the contract been performed successfully while deciding the matters where the defendant is liable to perform and the plaintiff is entitled to that performance.

Essential Requirements To Invoke The Maxim And Scope:

To invoke this maxim there are certain requisites which are listed below:

1. A contract for transfers of legal title
2. The contract should be a valid and enforceable
3. The suit should be brought by the parties within the limitation period
4. Evidence of existence of a valid contract

Scope of the maxim is limited to the rights of performance under the contract only and it applies to contractual obligations where the defendant has the liability to perform and the plaintiff is entitled to that performance, the maxim does not go beyond this limit.

Conclusion
The law of equity has evolved to grant equitable remedies and uphold natural justice which was generally the judge's discretion. The maxim of equity regards as done what should have been done deals with the cases where the right of plaintiff to receive performance of the contract and the court makes sure that the person gets equitable remedy and the contract is executed by making the defendant perform his part of the contractual obligations. This maxim is necessary to uphold the principle of justice, equity and good conscience.