Please remember that main difference between two is when profit will be booked.
Easy to remember is Cost method means it has cost so you need sales for profit.So you book profit when sales or re-issuance happens.
Par method is not cost method so you book profit when you buy from market.
It is probably best illustrated through a comparative example between the cost method and the par value method. Assume the following:
Company A issued 10,000 shares of common stock with a $10 par value when the market price was $35/share. Your entry to record the issuance would be as follows:
Dr. Cash 350,000
Cr. Common Stock 100,000
Cr. APIC – Common 250,000
The following transactions later occurred:
1) Company repurchased 2,000 shares of stock when the market price was $40/share.
2) Company reissued 1,000 shares of treasury stock when the market price was $45/share.
3) Company reissued another 1,000 shares of treasury stock when the market price was $30/share.
First, using the cost method:
1) Db. Treasury Stock 80,000
Cr. Cash 80,000
2) Db. Cash 45,000
Cr. Treasury Stock 40,000
Cr. APIC-treasury 5,000
3) Db. Cash 30,000
Db. APIC-treasury 5,000
Db. Retained Earnings 5,000
Cr. Treasury Stock 40,000
Remember that while you can debit APIC-treasury if you have a credit balance, you can never debit it “below zero”. Any difference is a debit to “Retained Earnings”.
Now for the par value method using the same transactions:
1) Db. Treasury Stock 20,000
Db. APIC-Common 50,000
Db. R/E 10,000
Cr. Cash 80,000
See what is occurring here. Treasury Stock is debited for 20,000 (2,000 shares times the par value of $10). APIC-Common is debited for 50,000 (the excess over par value paid for the 2,000 shares… remember that they were originally issued at $35/share; hence $35 minus $10 par value = $25, times 2,000 shares). The difference is debited to Retained Earnings (10,000, in this case).
2) Db. Cash 45,000
Cr. Treasury Stock 10,000
Cr. APIC-common 35,000
3) Db. Cash 30,000
Cr. Treasury Stock 10,000
Cr. APIC-common 20,000
You see that the subsequent re-issuance of treasury stock is extremely simple. You just credit Treasury Stock for par value, and then any difference is credited to APIC-common.