Use this calculator to estimate your chance of getting pregnant in one month (one cycle) and what that could mean over several months of trying. It is a simple probability estimate based on age, timing, and how regular your cycles are, not a diagnosis.
Advanced options
How to use this calculator
- Enter your Age (years).
- Enter how many months you plan to try (for example, 6).
- Choose whether your periods are usually regular or irregular.
- Select your Timing in the fertile window (best, typical, or uncertain).
- Open Advanced options if you want to (a) use your own per-cycle chance, (b) enter cycles per year for irregular cycles, or (c) show a low/typical/high range.
- Click Calculate.
- Read Chance per cycle used to see the per-try chance the model used after adjustments.
- Check Chance of getting pregnant within your planned months and the Chance of not being pregnant yet so you do not mistake odds for a guarantee.
- Use the 3, 6, and 12 month table to compare common timeframes under the same assumptions.
- Review the note on when to consider talking to a clinician for general guidance if you have been trying for a while or have very irregular cycles.
Definitions
Cycle: The time from the first day of one period to the first day of the next period.
Ovulation: When an ovary releases an egg.
Fertile window: The few days each cycle when pregnancy is most likely (around ovulation).
Per-cycle chance: The chance of pregnancy in one cycle when trying (one try).
Cumulative chance: The chance of getting pregnant at least once over many cycles.
Irregular cycles: Periods that are not predictable in timing; this can mean fewer chances per year.
Infertility: Not getting pregnant after a certain amount of time trying; definitions vary by age and situation. See general information from WHO and NICHD. [2] [3]
Methodology
What this calculator is doing
This tool starts with a typical per-cycle chance based on age, then adjusts it for timing in the fertile window. If you choose a custom per-cycle chance, it uses your number instead. It then converts that per-cycle chance into (1) an estimated chance per calendar month and (2) the chance of getting pregnant within a chosen number of months using standard probability math.
Step 1: Pick a baseline per-cycle chance from age
The calculator uses a simple age band lookup to choose a typical per-cycle chance. This is an average-style estimate for groups of people, not a prediction for one person.
Step 2: Apply timing adjustment (and cap)
Your timing selection applies a multiplier (for example, lower for uncertain timing and higher for best timing). The adjusted per-cycle chance is capped at 0.95 (95%) to avoid impossible-looking results. If the cap is reached, the calculator shows a short note.
Step 3: Handle irregular cycles with cycles per year
If cycles are irregular, the calculator uses your cycles per year to estimate cycles per month as cycles per year divided by 12. This helps avoid mixing up per-cycle and per-month chances when you do not have about one cycle each month.
Step 4: Convert per-cycle chance to per-month chance
If your expected cycles per month is not exactly 1, the calculator computes the chance in one calendar month as: per-month chance equals 1 minus (1 minus per-cycle chance) raised to the power of cycles per month.
Step 5: Chance within N months (and not pregnant yet)
The calculator estimates the number of cycles in your timeframe as months trying times cycles per month (this can be fractional). Then: chance within N months equals 1 minus (1 minus per-cycle chance) raised to the number of cycles. The chance of not being pregnant yet is the opposite: (1 minus per-cycle chance) raised to the number of cycles. This assumes each cycle is an independent try and the chance stays constant over time, which is a simplification.
Step 6: Months to about a 50% cumulative chance
To estimate months to reach about 50% cumulative chance, the calculator solves the cumulative formula for time using natural logs: months to 50% equals (ln(0.5) divided by ln(1 minus per-cycle chance)) divided by cycles per month. If the math would be undefined (like dividing by zero) or not finite, the result is shown as N/A.
Optional sensitivity range (low, typical, high)
If you turn on the range, the calculator builds a simple band around the typical per-cycle chance using plus or minus your chosen percentage points, with a tiny floor (epsilon) to avoid log(0), and the same 0.95 cap. It then recomputes the 3, 6, and 12 month cumulative chances for the low and high values. This range is only a sensitivity check to reduce false certainty, not a medical confidence interval.
Input checks and safe handling
Required inputs are strict: blank or non-numeric values are errors. If you select a custom per-cycle chance, the percent must be entered and must be between 1 and 99. If you select irregular cycles, cycles per year is required and must be between 1 and 20 to prevent divide-by-zero and unrealistic values. Very long time horizons still compute, but the constant-chance assumption becomes less realistic, so the calculator may show a brief note.
General guidance note
The output includes general guidance on when to consider talking to a clinician. This is educational and not a diagnosis. Guidance about infertility is described by public health and medical organizations. [2] [3]