What is the procedure for converting single entry bookkeeping to double entry bookkeeping?

Your question asks about converting single-entry bookkeeping to double-entry bookkeeping.  In order to convert single-entry bookkeeping to double-entry bookkeeping, it is helpful to first understand why the methods are used.

First, single-entry bookkeeping is generally used by small companies that need an economical record or their income and expenses.  The single-entry system consists of three accounts: personal, cash, and bank. There is no trial balance or balance sheet.  Profit and loss statements are not possible,...

Your question asks about converting single-entry bookkeeping to double-entry bookkeeping.  In order to convert single-entry bookkeeping to double-entry bookkeeping, it is helpful to first understand why the methods are used.

First, single-entry bookkeeping is generally used by small companies that need an economical record or their income and expenses.  The single-entry system consists of three accounts: personal, cash, and bank. There is no trial balance or balance sheet.  Profit and loss statements are not possible, and limited views of the transactions are available.

Double-entry bookkeeping can be considered more reliable for several reasons.  To begin with, each transaction is methodically recorded as a debit, then as a credit.  This is done so a trial balance can check accuracy of the entries, which shows income and expenditure accounts.

To convert single-entry to double-entry bookkeeping, you first need an opening statement of accounts.  From this you will post all of the transactions into a double-entry journal system as a debit, then as a credit. 

Next, you should open two bank accounts.  One should be for expenses, and the other for income.  Each of these accounts should have a double-entry debit and credit on your journal and ledgers.

From there, you will take two more steps.  Run a trial balance of the journal and ledger to assure that your entries are correct.  Then prepare an income statement to compare the single to double-entry balances.

Once everything is in balance, prepare a finalized balance sheet.

In summary, it is fairly challenging, but not impossible to convert a single-entry bookkeeping system to a double-entry bookkeeping system.  Either system should have an independent audit done regularly to ensure accuracy and to provide accountability.