Estimate when fertility returns after a 3-monthly DMPA shot (often called the Depo shot) using your last injection date, total injections, and whether a period has returned. Get median and 25th to 75th percentile months to ovulation, probability by month, first period timing, an approximate pregnancy-test date, and a care flag if no period by the threshold.
* The estimated date is 14 days after the early end of the estimated ovulation window. It is not a reliable personal test date or a date you need to wait for. Test from the first day of a missed period, or at least 21 days after the last unprotected sex if you do not know when your next period is due. The ovulation forecast is not a contraceptive protection schedule; follow your prescribed reinjection or alternative contraception schedule.
How this calculator works
- Inputs: date of last DMPA injection, total injections, period returned since the last shot (Y/N), optional age and BMI band.
- Outputs: estimated months to ovulation (median and 25th to 75th percentile), probability ovulation has returned by month X, expected timing of the first period, an approximate pregnancy-test date, and a care-flag if no period by the tool's threshold.
Methodology & limits
The model starts from typical return-to-ovulation patterns after DMPA and adjusts by reported injections and whether a period has returned. Age and BMI bands provide context. “Probability by month” is the chance that ovulation has happened by each month since the last shot. The first-period estimate follows the ovulation estimate with a typical luteal interval. The care-flag triggers at a set threshold within the tool.
The estimated pregnancy-test date adds 14 days to the early end (25th percentile) of the estimated ovulation window. It assumes ovulation and conception at that time, not a known conception date. For actual testing, follow NHS guidance: test from the first day of a missed period, or at least 21 days after the last unprotected sex if your next period date is unknown.
This estimate cannot diagnose conditions or predict individual results. For personalised guidance or prolonged amenorrhoea, speak with a clinician.
Frequently asked questions
Can I ovulate before my first period?
Yes. Ovulation can return before the first period. The estimated test date assumes conception when ovulation returns early; it does not tell you when you personally conceived. If your next period date is unknown, test at least 21 days after the last unprotected sex.
Do more injections delay return to fertility?
Longer use can extend the time to ovulation for some people. The model uses your total injection count in its estimate.
Why do you ask if a period has returned?
A recent period is a signal that ovulation has likely resumed. It narrows the estimate for the next ovulation window.
Do age and BMI affect the result?
They are used as context in the model. Age often has a larger effect on overall chances once ovulation returns.
When should I seek care?
The tool shows a care-flag if no period by its threshold. This is educational only. If you are concerned, see a clinician.
Pregnancy-test timing: NHS guidance on when to test.