According to Foreign Exchange Management act, 2000, you must surrender the unused foreign exchange within 180 days of your return from abroad. However, if you so desire you can keep foreign exchange up to USD 2,000 in your Resident Foreign Currency (Domestic) Account. You can keep the amount in foreign currency or traveller' cheque form.
But, if you have foreign coins then you need not surrender it to authorised brokers. You are eligible to keep foreign coins without any limit.
There is no limit on the amount of foreign currency a traveller can bring while returning to India. However, if the total value of the foreign exchange exceeds USD 10,000 in form of foreign currency and traveller's cheque or the traveller carries more than USD 5,000 in foreign currency alone then he/she has to declare it. It should be declared to the Custom Authorities at the Airport in the Currency declaration Form (CDF) on his/her arrival in India.
Foreign currency you can take on a business trip
If you are going abroad excluding Bhutan an Nepal on a business trip then you can carry foreign exchange up to $25,000. In case you need to carry over and above the limit then you have to take prior permission from the Reserve Bank of India (RBI).
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NRIs can carry INR 25,000 abroad
Non Resident Indians (NRIs) are eligible to carry up to Rs. 25,000 of Indian currency abroad. Earlier, only Indian residents were allowed to carry Indian currency notes up to Rs.10,000 out of the country.
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You should always be careful to surrender your forex amount after making a trip to abroad. Keeping foreign currency is a serious violation of the FEMA Act and could entail one landing in jail as well.