HesapHanem

Second Trimester Start Calculator

Enter the first day of your last menstrual period to find when your second trimester begins.

Result

2026-06-16
Week 14
98 days

How it is calculated

Enter the first day of your last menstrual period (LMP) as YYYY-MM-DD. The tool adds a fixed 98 days: start = LMP + 14 weeks × 7 days. That puts the start of gestational week 14, counted from the LMP and not from conception, on the date shown. The calendar is respected, including month ends and leap years. Impossible dates such as 30 February, and any format other than four-digit year, two-digit month and two-digit day, give no result. The answer does not depend on cycle length or on an ultrasound, and different clinics and sources may draw the trimester boundary a little differently.

Worked example

Say your LMP began on 10 March 2026 (2026-03-10). Add 98 days. From 10 March, 21 days reach 31 March, leaving 77. April has 30 days, leaving 47. May has 31, leaving 16. So 16 days into June is 16 June. The tool therefore shows a start date of 2026-06-16, which is gestational week 14 and 98 days after the LMP.

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Common mistakes

  • Entering the conception or ovulation date instead of the first day of the last period. This tool counts from the LMP, so using a date about two weeks later pushes the result about two weeks too late.
  • Using the last day of the period instead of the first day.
  • Typing the date as 10/03/2026 or 2026-3-10. Only the zero-padded form 2026-03-10 is accepted; other forms return nothing.
  • Treating the date as a medical deadline. It is a fixed 98-day calendar count, and your own provider may date your pregnancy from an early ultrasound instead.
  • Expecting the date to change with a longer or shorter cycle. The tool does not adjust for cycle length, so the 98 days stay the same.

Sources

About this calculator

Pregnancy is conventionally divided into three trimesters, and clinicians commonly mark the start of the second trimester at 14 weeks (98 days) from the first day of the last menstrual period — the same LMP-based dating convention used for due-date estimates like Naegele's rule.

The second trimester is often called the most comfortable stretch of pregnancy, as early symptoms like nausea typically ease and it's when anatomy scans and other routine second-trimester screenings are scheduled. Expectant parents and prenatal care providers use this milestone to plan checkups, screening windows, and simply to track where a pregnancy stands.

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Comments (1)

  • Editorial team

    If your clinic dated the pregnancy by ultrasound and gave you a due date, you can still use this: subtract 280 days from the due date and enter that as a stand-in LMP. A due date of 15 January 2027 gives 2026-04-10, and the tool then returns 2026-07-17. Your midwife or doctor has the final word on dating. Does your clinic count the second trimester from week 13 or week 14?

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