Live
Peptide Reconstitution / Dosage Calculator
Work out the concentration after reconstitution and how many units to draw on a U-100 insulin syringe for a prescribed dose.
Conception Date Calculator
Estimate when conception likely happened from your last period or due date, plus your fertile window.
Did we solve your problem today?
How to use this calculator
Enter your values after choosing the type of calculation in the tabs. The result updates as you type; press Calculate to confirm and jump to the result on mobile. Use Share to send the calculator with your result.
How conception is estimated
ovulation ≈ LMP + (cycle length − 14) days
due date = LMP + 280 days (+ cycle length − 28)
conception ≈ due date − 266 days
The luteal phase (ovulation to next period) is fairly constant at about 14 days, so a longer cycle moves ovulation later. A pregnancy lasts about 266 days (38 weeks) from conception, or 280 days (40 weeks) from the last period, the rule known as Naegele’s rule.
Fertile window
Pregnancy is possible from about 5 days before ovulation to 1 day after, because sperm can survive up to 5 days and the egg about 12–24 hours. The American College of Obstetricians and Gynecologists describes the same 6-day window.
Why ultrasound dating differs
First-trimester ultrasound measurements (crown-rump length) date a pregnancy to within about 5–7 days and are used to set the official due date when they disagree with the LMP date.
Frequently asked questions
How do I figure out when I conceived?
Add your cycle length minus 14 days to the first day of your last period, or subtract 266 days from your due date.
Can this tell who the father is?
No. Date estimates are too uncertain to establish paternity; only a DNA test can.
About this tool
- Written by
- [Author: to be assigned]
- Reviewed by
- Expert review pending
- Last updated
- 31 Oct 2026
See our methodology and editorial policy. Think something’s off? Report an error with this tool.
Related tools
All Health & FitnessLive
Body Fat Calculator
Estimate body fat percentage with the US Navy tape-measure method, plus fat mass, lean mass and your ACE category.
Live
Calorie (TDEE) Calculator
Estimate your daily calorie needs (BMR and TDEE) with the Mifflin-St Jeor equation, plus targets to lose or gain weight.
Live
One Rep Max (1RM) Calculator
Estimate your one-rep max (1RM) from a set of reps using the Epley, Brzycki and Lombardi formulas, with a percentage chart.
Live
Macro Calculator
Turn your calorie target into daily grams of protein, carbohydrate and fat for your goal and preferred macro split.
Live
BMI Calculator
Calculate adult body mass index (BMI) from height and weight, with the CDC weight category and healthy weight range.