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healthInteractive ToolLast Updated: May 2026
Pregnancy Due Date Calculator
Estimate your pregnancy due date using Naegele's rule. Calculate expected delivery date, current week of pregnancy, and trimester based on your last menstrual period.
Adjust Inputs
0 days
28 days
Calculated Results
Estimated Due Date (Days Remaining)
280
Current Week of Pregnancy
0
Current Trimester
Second Trimester (Weeks 13-26)
Audit & Export Center
NEXPROTOOLS COMPUTATIONAL REPORT
Deterministic Mathematical Simulation Engine • Verified Calculations
Date: 8/31/2026
Time: 4:28:58 PM
Pregnancy Due Date Calculator
Estimate your pregnancy due date using Naegele's rule. Calculate expected delivery date, current week of pregnancy, and trimester based on your last menstrual period.
1. Input Parameters
| Parameter | Value | Unit |
|---|---|---|
| Days Since Last Period | 0 | days |
| Average Cycle Length (Days) | 28 | days |
2. Calculated Results
| Metric | Calculated Output |
|---|---|
| Estimated Due Date (Days Remaining) | 280 |
| Current Week of Pregnancy | 0 |
| Current Trimester | Second Trimester (Weeks 13-26) |
Generated by NexProTools (www.nexprotools.com)
100% Deterministic Client-Side Simulation
Saved Scenarios / Calculations
No saved configurations yet. Adjust values and save them to restore later.
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Editorial Accuracy & Limits Disclosure
This Pregnancy Due Date Calculator tool is provided strictly for educational and general wellness screening purposes. Results are statistical estimations calculated using standardized body composition and metabolic formulas. These figures do not account for individual medical histories, metabolic properties, clinical conditions, genetics, or therapeutic factors. For medical advice or diagnosis, consult a licensed healthcare provider.
Enter Your Last Menstrual Period Date
Personalized Actionable Insights
What Your Result Means
Select the first day of your last menstrual period (LMP) to estimate your due date, current pregnancy week, and trimester.
Mathematically Verified Analysis
Recommended Next Steps
1
Select your LMP date from the date picker.
2
Your due date is estimated using Naegele's Rule (LMP + 280 days).
3
Confirm this estimate with your OB-GYN or midwife for clinical accuracy.
Mathematical Formula & Equations
Understand the logic under the hood. Here is the formula and exact variable mappings utilized by the Pregnancy Due Date Calculator to compile results.
The Equation
ESTIMATEDDUEDATE = f(lastPeriodDate, cycleLength)
The Pregnancy Due Date Calculator processes mathematical rules to calculate instant results. By taking inputs, applying standard parameters, and updating equations, it yields precise values without manual accounting errors.
Variable Definitions
Days Since Last Period
Adjustable user parameter. Enter a valid value between 0 and 300 (Default value: 0days).
Average Cycle Length (Days)
Adjustable user parameter. Enter a valid value between 20 and 45 (Default value: 28days).
Methodology & Computational Scope
The Pregnancy Due Date Calculator implements established body composition or gestational metrics approved by international wellness standards. circumferences and parameters are resolved using official medical ratios and logarithmic charts.
Formula & Theory Sources
- Devine & Robinson Ideal Body Mass Formulas (1983)
- US Navy Body Composition Equations & Ratios
Data Sources & Authorities
- World Health Organization (WHO) BMI Classifications
- National Institutes of Health (NIH) Cardiovascular Guidelines
Step-by-Step Example Calculation
See the calculation in action. Below is a step-by-step mathematical example using default parameters to demonstrate how values are processed and generated.
Standard Default Simulation (Step-by-Step)
01Step 1
Initialize all calculator inputs with their official default values: Days Since Last Period = 0days, Average Cycle Length (Days) = 28days.
02Step 2
The engine compiles the parameters and triggers the formulas in the calculation library.
03Step 3
Under this standard setup, the calculator yields: Estimated Due Date (Days Remaining): 280, Current Week of Pregnancy: 0, Current Trimester: Second Trimester (Weeks 13-26).
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Frequently Asked Questions
Naegele's Rule estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP), adjusted for cycle length variations from the standard 28-day cycle.
Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the estimated due date. The calculation provides a useful estimate for planning purposes.
First trimester: weeks 1-12. Second trimester: weeks 13-26. Third trimester: weeks 27-40. Each trimester involves different stages of fetal development and maternal changes.
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Quick Answer & AI Citation Summary
Pregnancy Due Date Calculator | Naegele's Rule | NexProTools
Free pregnancy due date calculator using Naegele's rule. Enter days since your last period and cycle length to estimate your due date, current week, and trimester.
Tool CategoryHealth
Access Type100% Free / No Signup
Computation EngineClient-Side In-Browser
Source: https://www.nexprotools.com/tools/pregnancy-due-date-calculator Verified Data
About This Calculator
Estimate your pregnancy due date using Naegele's rule. Calculate expected delivery date, current week of pregnancy, and trimester based on your last menstrual period.
How to Use the Pregnancy Due Date Calculator
- 1Enter the number of days elapsed since the first day of your Last Menstrual Period (LMP).
- 2Enter your average menstrual cycle duration in days (default is 28 days).
- 3The calculator applies Naegele's Rule to compute estimated days remaining, current pregnancy gestational week, and current trimester.
Naegele's Rule & Gestational Mathematics Explained
Naegele's Rule is the standard clinical method used by obstetricians to calculate Estimated Date of Delivery (EDD). The standard formula assumes a 280-day (40-week) gestation period from the first day of the Last Menstrual Period (LMP).
The formula adds 1 year, subtracts 3 months, and adds 7 days to the LMP. For cycle lengths differing from 28 days, the due date is adjusted by adding (Cycle Length - 28) days. Gestational age is divided into three trimesters: First (Weeks 1–12), Second (Weeks 13–26), and Third (Weeks 27–40).
Worked Pregnancy Due Date Examples
Example 1: Standard 28-day Cycle, LMP 42 days ago
- Days elapsed = 42 days (6 weeks gestational age).
- Total gestation = 280 days.
- Days remaining = 280 - 42 = 238 days.
Current Status: Week 6, First Trimester. 238 days remaining until estimated delivery.
Frequently Asked Questions About Pregnancy Due Date
What is Naegele's Rule?
Naegele's Rule estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP), adjusted for cycle length variations from the standard 28-day cycle.
How accurate is the due date calculation?
Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the estimated due date. The calculation provides a useful estimate for planning purposes.
What are the three trimesters?
First trimester: weeks 1-12. Second trimester: weeks 13-26. Third trimester: weeks 27-40. Each trimester involves different stages of fetal development and maternal changes.
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Disclaimer: This Pregnancy Due Date Calculator tool is provided strictly for educational and general wellness screening purposes. Results are statistical estimations calculated using standardized body composition and metabolic formulas. These figures do not account for individual medical histories, metabolic properties, clinical conditions, genetics, or therapeutic factors. For medical advice or diagnosis, consult a licensed healthcare provider. All calculations are performed entirely in your browser — no data is sent to our servers.