Build a Pregnancy Conception Calculator 👶
Most calculators tell you when the baby is due. This one works backwards: "When did it happen?" This allows parents to estimate the date of conception based on their due date or ultrasound results.
Step 1: The Math (Reverse Engineering) 🧮
Medical standard pregnancy is 280 days (40 weeks) from the Last Menstrual Period (LMP). However, conception usually happens ~14 days after the LMP (during ovulation). So, fetal development is actually 266 days (38 weeks).
Formulas:
- From Due Date:
Conception = Due Date - 266 Days - From LMP:
Conception = LMP + 14 Days - From Ultrasound:
Conception = Ultrasound Date - (Weeks Pregnant * 7 Days)
Step 2: Sperm Viability (The Window) ⏳
Conception isn't just a single moment; it's a window. Sperm can live inside the body for up to 5 days. So, if the calculated conception date is Day X, intercourse likely occurred between Day X-5 and Day X.
Step 3: The React Component 📅
We need a flexible input that handles different known dates.
"use client"
import { useState } from "react"
import { Calendar, Baby } from "lucide-react"
export default function ConceptionCalc() {
const [mode, setMode] = useState<'due' | 'lmp'>('due')
const [date, setDate] = useState("")
const [result, setResult] = useState<Date | null>(null)
const calculate = () => {
if (!date) return;
const inputDate = new Date(date + 'T12:00:00'); // Fix UTC shift
if (mode === 'due') {
// Subtract 266 days
inputDate.setDate(inputDate.getDate() - 266);
} else {
// Add 14 days to LMP
inputDate.setDate(inputDate.getDate() + 14);
}
setResult(inputDate);
}
return (
<div className="max-w-md mx-auto p-6 bg-rose-50 rounded-xl border border-rose-100 shadow-sm">
<div className="flex justify-center gap-4 mb-6">
<button
onClick={() => setMode('due')}
className={`px-4 py-2 rounded-full text-sm font-bold transition ${mode === 'due' ? 'bg-rose-500 text-white' : 'text-rose-400 hover:bg-rose-100'}`}
>
I know Due Date
</button>
<button
onClick={() => setMode('lmp')}
className={`px-4 py-2 rounded-full text-sm font-bold transition ${mode === 'lmp' ? 'bg-rose-500 text-white' : 'text-rose-400 hover:bg-rose-100'}`}
>
I know LMP
</button>
</div>
<div className="mb-6">
<label className="block text-xs font-bold text-rose-400 uppercase mb-2">
{mode === 'due' ? 'Your Due Date' : 'First Day of Last Period'}
</label>
<input
type="date"
value={date}
onChange={e => setDate(e.target.value)}
className="w-full p-3 border border-rose-200 rounded-lg focus:ring-2 focus:ring-rose-400 outline-none text-rose-900"
/>
</div>
<button
onClick={calculate}
disabled={!date}
className="w-full py-4 bg-rose-500 text-white font-bold rounded-lg hover:bg-rose-600 transition disabled:opacity-50"
>
CALCULATE CONCEPTION
</button>
{result && (
<div className="mt-8 text-center animate-in zoom-in duration-300">
<div className="w-16 h-16 bg-white rounded-full flex items-center justify-center mx-auto mb-4 shadow-sm text-rose-500">
<Baby size={32} />
</div>
<div className="text-sm font-medium text-rose-400 uppercase">Estimated Conception Date</div>
<div className="text-3xl font-black text-rose-600 my-2">
{result.toLocaleDateString('en-US', { month: 'long', day: 'numeric', year: 'numeric' })}
</div>
<div className="p-4 mt-4 bg-white/50 rounded-lg text-xs text-rose-800">
<span className="font-bold">Note:</span> Intercourse likely happened
within the <span className="underline decoration-dotted">5 days leading up to this date</span>.
</div>
</div>
)}
</div>
)
}
Step 4: Medical Disclaimer ⚕️
Always include a disclaimer.
"This tool provides an estimate based on a standard 28-day cycle. Ovulation timing varies for every individual. Ultrasound dating remains the most accurate method."