القسط الشهري على حسب مدة السداد.

A natural Egyptian-style pronunciation would be:

el-'est esh-shahri ʿala 7asab moddet es-sadad

A few useful pronunciation notes:

• القسط is often pronounced el-'est in Egyptian, because ق is commonly pronounced like a glottal stop.
• الشهري becomes esh-shahri, not el-shahri, because ش is a sun letter, so the l in الـ assimilates.
• مدة is pronounced modda by itself, but here it becomes moddet because it is followed by another noun in a possessive-type structure: مدة السداد.

Because in Arabic, adjectives usually come after the noun they describe.

So:

• القسط = the installment
• الشهري = monthly

Together:

• القسط الشهري = the monthly installment

This is the normal Arabic word order:

• noun first
• adjective second

Also, the adjective must match the noun in definiteness. Since القسط has الـ, the adjective also has الـ:

• القسط الشهري not
• القسط شهري

على حسب means depending on, according to, or based on.

In this sentence, it introduces the factor that the monthly installment changes with:

• على حسب مدة السداد = depending on the repayment period

In Egyptian Arabic, على حسب is very common in everyday speech. It can be used in lots of situations, for example:

• السعر على حسب الكمية = The price depends on the quantity.
• المعاد على حسب الظروف = The موعد depends on the circumstances.

So here it gives the idea of variation based on something.

Because Arabic often leaves out the present-tense verb to be.

This is very normal. The sentence is understood as something like:

• The monthly installment is according to the repayment period or more naturally in English:
• The monthly installment depends on the repayment period

Arabic does not always need an explicit verb in the present tense. The relationship is understood from the structure.

If someone wanted to say it more explicitly in Egyptian Arabic, they might say:

• القسط الشهري بيتحدد على حسب مدة السداد
  = The monthly installment is determined based on the repayment period.

But the shorter version is completely normal, especially in formal or business contexts.

مدة السداد is an iḍāfa construction, often explained as a possessive or noun-linking structure.

It is made of:

• مدة = duration / period
• السداد = the repayment / the paying-off

Together:

• مدة السداد = the repayment period
• literally: the duration of repayment

A key point about this structure:

• the first noun usually does not take الـ
• the second noun can be definite

So Arabic says:

• مدة السداد not
• المدة السداد

Also, because مدة is followed by another noun in iḍāfa, the ة is pronounced as t, giving moddet es-sadad.

That final ة is called tāʾ marbūṭa.

When a word ends in ة, it is often pronounced like -a when said alone:

• مدة by itself: modda

But when that word is followed by another noun in an iḍāfa construction, the ة is pronounced as -t:

• مدة السداد = moddet es-sadad

This is very common in Arabic. Compare:

• شركة = shérka
• شركة التأمين = shirket et-ta'mīn

So in your sentence, the t sound is there because مدة is linked to السداد.

In this context, السداد means repayment, settlement, or paying off an amount owed.

It is often used in financial situations such as:

• loans
• installments
• bills
• debts

الدفع is a more general word for payment or paying.

So:

• الدفع = paying in general
• السداد = paying off what is owed, often in a more formal or financial sense

That is why مدة السداد sounds especially appropriate in banking, financing, and installment plans.

It sits in a space that works in both.

The vocabulary and structure are quite neutral and formal, so you could easily see or hear this in:

• Egyptian business speech
• advertisements
• banking or financing language
• written Arabic

What makes it feel Egyptian is mainly the pronunciation, especially:

• ق often becoming a glottal stop
• everyday use of على حسب

A more explicitly conversational Egyptian version might be:

• القسط الشهري بيتحدد على حسب مدة السداد
• قيمة القسط الشهري على حسب مدة السداد

But the sentence you have is perfectly natural in Egyptian contexts.

Because the adjective has to match the noun in definiteness.

Here:

• القسط = the installment
• الشهري = the monthly → really just monthly, but marked definite to agree with the noun

In Arabic, if the noun is definite, the adjective must also be definite.

So:

• قسط شهري = a monthly installment
• القسط الشهري = the monthly installment

This agreement is one of the main things English speakers need to get used to.

Because ش is a sun letter.

When الـ comes before a sun letter, the l sound is not pronounced. Instead, the following consonant is doubled.

So:

• written: الشهري
• pronounced: esh-shahri

This is the same pattern as in words like:

• الشمس → esh-shams
• الشارع → esh-shāreʿ

It is written the same way, but pronounced with assimilation.

Yes, you can, but the nuance and style may shift slightly.

• حسب مدة السداد is also correct and often sounds a bit more formal or written.
• على حسب مدة السداد is very common in speech, including Egyptian Arabic.

So both are possible, but:

• على حسب often feels more conversational
• حسب alone can feel a little more concise or formal

In everyday Egyptian usage, على حسب is extremely common.

القسط usually refers to an installment: one part of a larger amount paid over time.

It is common with:

• loans
• financing
• tuition
• insurance
• purchases paid in parts

So it is broader than just loans. For example, it can refer to:

• a monthly installment for a car
• a tuition installment
• an insurance premium installment

In financial Egyptian Arabic, القسط الشهري is a very common phrase.