Pregnancy Check Calculator
When To Take a Pregnancy Test Calculator works out Earliest an early-result test is labelled for and First day of a missed period from Date I know, First day of my last period and Ovulation date. The default figures on this page give first day of a missed period of 2025-03-30; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
6 steps
- Ovulation is one luteal phase before the next period, so on cycle day 28 - 14 = 14: 2025-03-15.
- The next period is due 28 days after the last one started: 2025-03-29.
- Implantation happens 6 to 12 days after ovulation, so between 2025-03-21 and 2025-03-27.
- The earliest day an "early result" test is labelled for is 5 days before the period is due: 2025-03-24.
- A missed period starts the day after it was due: 2025-03-30. By then implantation has happened in 90% of pregnancies.
- One week later, 2025-04-06, that has risen to 97%, which is when a negative test is worth believing.
Day-by-daytable
| date | weekday | milestone | detection |
|---|---|---|---|
| 2025-03-24 | Monday | 5 days before the period is due | >=76% |
| 2025-03-25 | Tuesday | 4 days before the period is due | 96% |
| 2025-03-26 | Wednesday | 3 days before the period is due | >99% |
| 2025-03-27 | Thursday | 2 days before the period is due | >99% |
| 2025-03-28 | Friday | 1 day before the period is due | >99% |
| 2025-03-29 | Saturday | The day the period is due | >99% of samples from pregnant women, per the package insert |
| 2025-03-30 | Sunday | First day of a missed period | 90% of pregnancies have implanted by now (Wilcox 2001) |
| 2025-04-06 | Sunday | One week after the missed period | 97% have implanted; a negative here is meaningful (Wilcox 2001) |
Its 4 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
3 sources
What the When To Take a Pregnancy Test Calculator calculates
Works out the earliest day a home pregnancy test could be positive, the day of the missed period and the day a negative result becomes trustworthy, from the implantation window and the published detection rates rather than a rule of thumb.
How to use this When To Take a Pregnancy Test Calculator
Enter Date I know, First day of my last period, Ovulation date and Embryo transfer date. Earliest an early-result test is labelled for updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Earliest an early-result test is labelled for, First day of a missed period and A negative becomes trustworthy.
The method follows Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy, Wilcox AJ, Baird DD, Dunson D, McChesney R, Weinberg CR. Natural limits of pregnancy testing in relation to the expected menstrual period and FIRST RESPONSE Early Result Pregnancy Test - package insert, Church & Dwight Co., Inc..
Textbook 28-day cycle, last period 1 March 2025 example
With Date I know: lmp, First day of my last period: 2025-03-01, Usual cycle length: 28, Luteal phase length: 14, the calculator returns Estimated ovulation: 2025-03-15, Period due: 2025-03-29, Earliest an early-result test is labelled for: 2025-03-24. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Earliest an early-result test is labelled for, First day of a missed period and A negative becomes trustworthy. The inputs you can vary are Date I know, First day of my last period, Ovulation date, Embryo transfer date, Embryo age at transfer and Usual cycle length.
Understanding Earliest an early-result test is labelled for, First day of a missed period and A negative becomes trustworthy
An estimate from calendar arithmetic, not a clinical assessment. Only about 4% of births occur on the estimated due date; ultrasound dating by a clinician supersedes menstrual dating when they disagree. A negative test before the missed period means very little - about 10% of pregnancies have not implanted by then and cannot yet be detected by any test. Confirm any positive with a clinician, and seek urgent care for severe one-sided pain or heavy bleeding, which can signal an ectopic pregnancy.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
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Frequently asked questions
How far along can you detect a pregnancy?
On the figures this page opens with, the first day of a missed period is 2025-03-30. No single number fits everyone: it follows Date I know, First day of my last period and Ovulation date, so enter your own above and the answer updates as you type.
What information do I need for the When To Take a Pregnancy Test Calculator?
You need Date I know, First day of my last period, Ovulation date, Embryo transfer date, Embryo age at transfer, Usual cycle length, Luteal phase length and Today's date. The page opens with default figures that give first day of a missed period of 2025-03-30, so you can see the scale before entering your own.
What does this When To Take a Pregnancy Test Calculator show?
It shows Earliest an early-result test is labelled for, First day of a missed period, A negative becomes trustworthy, Estimated ovulation, Period due, Implantation window opens, Implantation window closes and Days until the earliest test date, with the working and any warnings for your entries.
Can I check how the When To Take a Pregnancy Test Calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.