A pregnancy calculator can estimate a due date and pregnancy timeline from a known starting date. Tervilo's pregnancy calculator is an educational date calculator, not a substitute for prenatal care. The result depends on the date entered and the dating assumptions used by the calculation.
What the pregnancy calculator helps you understand
A pregnancy calculator is broader than a single due-date calculation. It can organize a rough pregnancy timeline, relate dates to gestational weeks, and explain how the selected dating method anchors that timeline.
How to use Tervilo's Pregnancy Calculator
- Open the Tervilo Pregnancy Calculator.
- Select the available dating method.
- Enter the relevant date.
- Review the estimated due date or pregnancy timeline.
- Use the output as a reference for planning and questions for your healthcare provider.
Why dates are estimates
Ovulation and conception do not always occur on a fixed schedule, and menstrual-cycle length varies. This means a calculation based on a standard timing assumption cannot identify the exact biological date for every pregnancy.
LMP-based dating
The first day of the last menstrual period is often used as a practical reference because it is easier to remember than the exact conception date. The estimate is less certain when the LMP is unknown, cycles are irregular or bleeding was not a typical period.
Why pregnancy timelines can differ
Cycle variation, uncertainty about the starting date, and later clinical dating can change the estimated timeline. These differences do not automatically indicate a calculation error.
Why clinical dating can differ
Healthcare professionals may revise pregnancy dating using clinical history and ultrasound findings. ACOG recommends using the best available information to establish and document the estimated due date. ACOG pregnancy dating guidance.
Example
If a person enters a known LMP date, the calculator produces an estimated due date based on that date. Another method based on conception can produce a different result because it uses a different starting point. The difference does not automatically mean that either calculation is “wrong.”
Using the result responsibly
Use the date to understand a rough pregnancy timeline, prepare questions and organize appointments. Do not use the calculator to make decisions about symptoms, medicines, delivery timing or pregnancy complications.
When the calculator is not enough
Contact a qualified healthcare professional for prenatal questions or symptoms. Pregnancy calculators cannot evaluate the health of a pregnancy, the growth of a fetus or whether a pregnancy complication is present.
What can make a pregnancy estimate less certain?
Irregular cycles, uncertainty about the LMP, variable ovulation timing and incomplete date information can all affect a calendar estimate. This is why a result should be treated as an approximate timeline rather than an exact biological measurement.
How to keep your calculation understandable
Record which starting date you used and which method the calculator applied. If a healthcare professional later gives you a revised estimated due date, you can compare the two dates without assuming that a difference means the original calculator was malfunctioning.
Quick checklist
- □ I know which dating method I selected.
- □ I entered the correct date.
- □ I understand the output is an estimate.
- □ I understand clinical dating can change the estimated date.
- □ I use professional care for pregnancy decisions.
Quick answer
A pregnancy calculator estimates a due date and timeline from an LMP or another supported starting date. It is useful for general planning, but pregnancy dating can be revised when clinical information provides a better estimate.