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Blastocyst conversion rate calculator

How many embryos reached day 5?

Q: Is a low rate my fault?

No. It usually reflects egg quality, which tracks age, and sometimes sperm DNA integrity. Neither is something you caused or could have prevented by doing anything differently during the cycle.

Q: Should we transfer on day 3 instead?

If very few embryos are available, some units transfer earlier rather than risk none surviving to day 5. It is a genuine clinical judgement with reasonable arguments on both sides — worth asking directly what your unit would do and why.

Q: Should we test the blastocysts we have?

It depends on how many there are and your age. With one or two blastocysts, testing may leave you with nothing to transfer. The right questions are what evidence supports it for your specific situation, and what you would do differently based on the result.

How many fertilised embryos reached the blastocyst stage. The strongest signal a cycle gives about embryo quality.

Blastocysts on day 5 or 6

Usable blastocysts

Normally fertilised (2PN)

Embryos that fertilised

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

Example answer

43%

35–50%

Within the commonly reported range. Around 40 to 50 percent is a frequently quoted average across mixed populations.

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.

Reached blastocyst: 3
Fertilised embryos: 7
Arrested in culture: 4

What each result means

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

Your result<20%

Low. High attrition in culture points toward egg quality, sperm DNA integrity, or laboratory conditions. Worth a specific conversation before repeating the same protocol.

Your result20–35%

Below what many units expect, though not unusual with lower egg numbers or higher maternal age.

Your result35–50%

Within the commonly reported range. Around 40 to 50 percent is a frequently quoted average across mixed populations.

Your result50%+

A good conversion rate. Embryo development is unlikely to be the limiting factor in this cycle.

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

During an IVF cycle

Make sense of the numbers your clinic gives you.

Medicines
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Egg collection
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Your embryos

This calculator: How many embryos reached day 5?

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.

Blastocyst conversion rate is blastocysts divided by fertilised embryos, and is the strongest single signal about embryo quality. Around 40 to 50% is commonly reported, and the rate declines with maternal age.

About this calculator

?What it tells you

Blastocyst rate. How many fertilised embryos reached the blastocyst stage. The strongest signal a cycle gives about embryo quality.

✓When to use it

On day 5 or 6, the most informative number of the cycle

iWhat you need

Blastocysts on day 5 or 6
Normally fertilised (2PN)

!What it cannot tell you

Blastocyst rates decline with maternal age and differ between laboratories.

Common questions

Is a low rate my fault?

No. It usually reflects egg quality, which tracks age, and sometimes sperm DNA integrity. Neither is something you caused or could have prevented by doing anything differently during the cycle.

Should we transfer on day 3 instead?

If very few embryos are available, some units transfer earlier rather than risk none surviving to day 5. It is a genuine clinical judgement with reasonable arguments on both sides — worth asking directly what your unit would do and why.

Should we test the blastocysts we have?

It depends on how many there are and your age. With one or two blastocysts, testing may leave you with nothing to transfer. The right questions are what evidence supports it for your specific situation, and what you would do differently based on the result.

Sources

Conversion rates fall with maternal age and vary between laboratories. Compare against your own unit’s figures for your age band.

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.