The 11 month convention is not superstition. It is a direct consequence of two statutory provisions.
The registration rule
Section 17 of the Registration Act, 1908 makes registration compulsory for leases of immovable property from year to year, or for a term exceeding one year, or reserving a yearly rent. Section 107 of the Transfer of Property Act, 1882 requires such a lease to be made by a registered instrument. A term of 11 months falls below the threshold, so registration is not compulsory and stamp duty is lower.
Is it valid
Yes. An 11 month agreement is a perfectly valid contract between the parties. It can be renewed by a fresh agreement, which is why these documents are re-executed year after year.
An unregistered instrument that ought to have been registered is largely inadmissible in evidence under Section 49 of the Registration Act, save for limited collateral purposes. So a two or three year "rent agreement" left unregistered is worse than useless if there is ever a dispute about its terms. If you genuinely want a longer term, register it and pay the duty. Do not write a three year term and skip registration.
Lease or leave and licence
A lease transfers an interest in the property and gives the tenant exclusive possession. A leave and licence gives only permission to occupy, without transferring an interest. Which one you have depends on the substance of the arrangement rather than the label at the top of the page, and courts look at whether exclusive possession was in fact given.
What a good agreement should contain
- Term, rent, due date, mode of payment, and escalation on renewal
- Security deposit, and a clear timeline and conditions for refund. Deposit disputes are the single most common landlord and tenant fight
- Notice period on both sides, and lock-in if any
- Who pays maintenance, property tax, and utility charges
- Permitted use, and whether subletting is allowed
- An inventory of fittings, and the position on damage and normal wear and tear
- Rules on entry by the landlord for inspection
Pay rent and deposit by bank transfer. When a dispute arises, the bank record is what decides it.