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Follicular output rate (FORT) calculator

Did my follicles respond well?

Q: How is this different from AMH or AFC?

Those measure how many follicles are available. FORT measures how many of them actually responded. Someone can have a reasonable AFC and a poor FORT, which points at the protocol rather than at reserve.

Q: Can FORT be improved?

Sometimes. It is one of the findings that prompts a change of stimulation approach rather than a change in expectations, which makes it a useful thing to ask about after a disappointing cycle.

Q: Is a low FORT the same as poor reserve?

No, and the distinction matters. Reserve is how many follicles you have; FORT is how many of them responded. A normal antral count with a low FORT points at the stimulation protocol, which is adjustable — that is a much more hopeful finding than low reserve.

How many antral follicles actually responded to stimulation. A measure of follicular sensitivity rather than of reserve.

Pre-ovulatory follicles

16–22mm on trigger day

Antral follicle count

At baseline scan

These are example numbers. Replace them with yours, then press Calculate.

Example answer

64%

60%+

Good follicular response — most of the available cohort responded to stimulation.

This is a guide, not a diagnosis. Share the result with your doctor.

Your result on the scale

The ranges this calculator uses. Yours is highlighted.

Your numbers

Everything worked out from what you entered.

Pre-ovulatory follicles: 9
Antral follicle count: 14
Did not respond: 5

What each result means

Your result is highlighted. Your own clinic's advice always comes first.

Your result<40%

Low FORT. Suggests follicles present at baseline did not respond well to stimulation, which is a protocol question rather than a reserve question.

Your result40–60%

Intermediate. Commonly reported and not in itself concerning.

Your result60%+

Good follicular response — most of the available cohort responded to stimulation.

Where this fits in your journey

The usual order, from trying to conceive to pregnancy. Not everyone needs every stage. This calculator belongs to stage 4.

Stage 4 · you are here

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This calculator: Did my follicles respond well?

Calculators for what comes next

How this is worked out

Exact calculationArithmetic on the numbers you enter. If your inputs are right, this figure is right.

Follicular output rate is the number of pre-ovulatory follicles divided by the antral follicle count, showing how many available follicles actually responded to stimulation. A low FORT points at the protocol rather than at ovarian reserve.

About this calculator

?What it tells you

Follicular output rate (FORT). How many antral follicles actually responded to stimulation. A measure of follicular sensitivity rather than of reserve.

✓When to use it

After a disappointing cycle, to see whether the protocol is the issue

iWhat you need

Pre-ovulatory follicles
Antral follicle count

!What it cannot tell you

FORT is a research-derived index used alongside clinical judgement, not a standalone measure.

Common questions

How is this different from AMH or AFC?

Those measure how many follicles are available. FORT measures how many of them actually responded. Someone can have a reasonable AFC and a poor FORT, which points at the protocol rather than at reserve.

Can FORT be improved?

Sometimes. It is one of the findings that prompts a change of stimulation approach rather than a change in expectations, which makes it a useful thing to ask about after a disappointing cycle.

Is a low FORT the same as poor reserve?

No, and the distinction matters. Reserve is how many follicles you have; FORT is how many of them responded. A normal antral count with a low FORT points at the stimulation protocol, which is adjustable — that is a much more hopeful finding than low reserve.

Sources

FORT was described by Genro et al. Cut-offs used in the literature vary; the low/intermediate/high tertile split is the most common presentation.

Genro et al., follicular output rate (FORT)

In an emergency

If you have any of the warning signs listed here, don't wait for a test result or a calculator. Get help now.

112All emergencies, anywhere in India 108Ambulance

Also call your IVF clinic. Most clinics give an emergency number on your treatment or discharge sheet. Save it in your phone now, before you need it.