How to calculate interest on a Credit Union loan

I am considering borrowing approx €3000.
Repayment over approx 1 year, paying €50/week.
18 months if €40/week.
2 years if €30/week.

Could someone tell me how interest is calculated/accumulated and how much this loan amount would cost me in total over 1 year, or 18 months or longer..? (I've heard it can be very expensive but I don't know how it works).

I already have just over a third in shares, which I may use to pay off the final part of the loan so it's really only the first €2000 or so + interest that I'd have to worry about.

Thanks for any replies.

Have your credit union told you what the interest rate is?

Hi Paddy. No I haven't asked them about borrowing yet.
But it's a small branch so I imagine that would mean interest would be a bit higher than one of the larger ones.
I'm really just looking for a rough idea of what the average CU loan would cost and how it's calculated over time.

You could google for "credit union loan calculator" and get many sites like this: [broken link removed]. Then you can play with numbers.

[There isn't really such a thing in Ireland as a small branch of a CU: there are small CUs, but each CU is a standalone operation.]