How long did Abraham and Sarah have to wait for Isaac?

from the old testament

• When Abraham (then known as Abram) was seventy-five years old, God called him to leave his homeland and journey to a land God would show him. In return, God promised, "I will make of you a great nation, and I will bless you and make your name great, so that you will be a blessing" (Genesis 12:2).
• Abram, his wife Sarai (later known as Sarah), and his nephew Lot then traveled to Canaan where God promised, "To your offspring I will give this land" (Genesis 12:7). Due to a famine in the land, Abram and Sarai continued on to Egypt. When they returned to the land of Canaan, God expounded on His promise saying, "I will make your offspring as the dust of the earth, so that if one can count the dust of the earth, your offspring also can be counted" (Genesis 13:16).
• Some time later, Abram confronted God and said, "O Lord GOD, what will you give me, for I continue childless" (Genesis 15:2). But God confirmed, "'your very own son shall be your heir.' And he brought him outside and said, 'Look toward heaven, and number the stars, if you are able to number them.' Then he said to him, 'So shall your offspring be'" (Genesis 15:4–5).
• However, the Bible records that ten years after Abram had returned from Egypt, he and his wife remained childless. At this time, "Sarai, Abram's wife, took Hagar the Egyptian, her servant, and gave her to Abram her husband as a wife" (Genesis 16:3). Hagar became pregnant and "Abram was eighty-six years old when Hagar bore Ishmael to Abram" (Genesis 16:16).
• But Ishmael was not the child God intended to receive the covenant. "When Abram was ninety-nine years old the LORD appeared to Abram and said to him, '…I may make my covenant between me and you, and may multiply you greatly…and you shall be the father of a multitude of nations'" (Genesis 17:1–2, 4).
• At this time, God also changed his name from Abram to Abraham and his wife's from Sarai to Sarah. He added "I will bless her, and moreover, I will give you a son by her. I will bless her, and she shall become nations; kings of peoples shall come from her" (Genesis 17:16).
• God also directed, "Sarah your wife shall bear you a son, and you shall call his name Isaac… I will establish my covenant with Isaac, whom Sarah shall bear to you at this time next year" (Genesis 17:19, 21).
• After Abraham obeyed God in the covenant of circumcision, the promise was repeated to him by heavenly visitors: "I will surely return to you about this time next year, and Sarah your wife shall have a son" (Genesis 18:10). The Bible records, "And Sarah conceived and bore Abraham a son in his old age at the time of which God had spoken to him" (Genesis 21:2). It then confirms, "Abraham was a hundred years old when his son Isaac was born to him" (Genesis 21:5). So Abraham was first promised descendants twenty-five years before Isaac's birth. However, when God provided the name of Isaac and a timeline of one year until his birth, it came true just as He said.

from the new testament

• The New Testament reflects on Abraham and Sarah’s long wait for Isaac as an example of God’s faithfulness and the power of His promises, but it doesn’t give a precise timeline like the Old Testament does. It emphasizes trust in God’s timing and the role of faith. For example, Romans 4:18–21 highlights Abraham’s faith: he “did not waver in unbelief at God’s promise but was strengthened in faith and gave glory to God, being fully persuaded that God had power to do what he had promised.” Abraham trusted God despite the long wait.
• In Hebrews 11:11–12, Sarah is commended for receiving the ability to conceive “by faith,” even though she was past the normal age for childbearing, showing God’s miraculous timing.
• God’s promises come according to His purposes, not human timing. Abraham’s faith and God’s promise to him are cited as the foundation of blessing for all who trust God (Galatians 3:7–9).

implications for today

There is often a delay between God's promise and its fulfillment. There were twenty years between Joseph's dreams and the time his brothers and father bowed before him in Egypt (Genesis 37:2; 41:46, 53). David was a teenager when Samuel anointed him the next king of Israel, but "David was thirty years old when he began to reign" (2 Samuel 5:4). There were more than four hundred years between God's promise of a Messiah and Jesus' birth. Even the disciples had to wait about nine days between Jesus' ascension and the outpouring of the promised Holy Spirit (Acts 1:3; 2:1).

Although there may have been a delay between the promise and the fulfillment, God has always been faithful to keep His promises. Joshua 21:45 records, "Not one word of all the good promises that the LORD had made to the house of Israel had failed; all came to pass." Paul assured the Corinthians in 2 Corinthians 1:20, "For all the promises of God find their Yes in [Jesus Christ]." So God is faithful to fulfill His promises, even if it took twenty-five years in the case of Abraham and Sarah. Both Abraham and Sarah are mentioned as examples of faithful believers in the "Hall of Faith" listed in Hebrews 11. In reference to their long wait for Isaac, Hebrews 11:11 says, "By faith Sarah herself received power to conceive, even when she was past the age, since she considered him faithful who had promised." May we similarly place our trust in this faithful God.