To calculate whether a savings-to-checking account would be financially worth your while at any of the area banks surveyed, you should first determine your average balance and the average number of checks written monthly.

Your average balance runs about 2 1/2 times your minimum balance. If you make a regular deposit, add half of that deposit to the minimum balance and divide by two to get the average. For example, if the lowest balance last month in your checking account was $300 and your weekly paycheck is $500 ($2,000 monthly), your average monthly balance is $650.

Average the number of checks written over the past several months from stubs or bank statements. If AFT, banks customarily make one transfer charge per day per account no matter how many checks clear.

To calculate the transfer charge, multiply the number of checks up to 5 by 1; between 6 and 10 checks, multiply by 0.9; and between 11 and 25 checks, 0.8. Anything over 26 checks will equal 20 transfers.

Then multiply your average balance by the interest rate paid. (A very few banks pay interest only on the minimum balance, so be sure to note the basis for payment.)

Next add the monthly service charge if there is a flat fee or if your balance is low enough to trigger a charge. Then calculate the transfer charges, if any. Multiply both figures by 12 and subtract from the annual interest paid. MONTHLY FEE: $0 Central National Bank of Maryland: Interest rate: 5% Minimum balance: $1,000 Transfer fee: Line of credit at 15% APR under $1,000 balance. Guaranty Bank & Trust: Interest rate: 5 1/4% Minimum balance: None Transfer fee: $1 McLean Bank: Interest rate: 5 1/4% Minimum balance: $1,500 Transfer fee: $1 National Savings and Trust: Interest rate: 5 1/4% Minimum balance: None Transfer fee: $1 Union Trust Bank: Interest rate: 5 1/4% Minimum balance: None Transfer fee: $1 MONTHLY FEE: $1 First Merchants National Bank: Interest rate: 5 1/4% Minimum balance: $5,000 Monthly fee applied to: Balances from $2,500 to $5,000 MONTHLY FEE: $2 Burke and Herbert Bank & Trust Co.: Interest rate: 5 1/4% Minimum balance: None Monthly fee applied to: All balances up to $2,500 Transfer fee: 25 cents Transfer fee applied to: All balances First American Bank: Interest rate: 5 1/4% Minimum balance: $5,000 Monthly fee applied to: Balances from $2,000 to $5,000 Transfer fee: 50 cents per day First Merchants Bank: Interest rate: 5 1/4% Minimum balance: $5,000 Monthly fee applied to: Balances from $1,500 to 2,500 Transfer fee: None MONTHLY FEE: $3 Citizens National Bank: Interest rate: 5 1/4% Minimum balance: $1,000 Monthly fee applied to: Balances from $1,000 to $1,500 Transfer fee: None First Commercial Bank: Interest rate: 5 1/4% Minimum balance: None Monthly fee applied to: All balances Transfer fee: 25 cents First Merchants Bank: Interest rate: 5 1/4% Minimum balance: $5,000 Monthly fee applied to: Balances from $500 to $1,000 Transfer fee: None First Virginia Bank: Interest rate: 5% Minimum balance: $500 Monthly fee applied to : Balances up to $500 Transfer fee: None Northern Virginia Bank: Interest rate: 5 1/4% Minimum balance: $1,000 Monthly fee applied to: Balances up to $1,000 Transfer fee: 25 cents Transfer fee applied to: All balances United National Bank of Washington Interest rate: 5% Minimum balance: $500, (checking); $150, (savings) Monthly fee applied to: Balances up to $500 Transfer fee: None MONTHLY FEE: $4 Bank of Virginia: Interest rate: 0 to 5 1/4%* Minimum balance: $500 Monthly fee applied to: Balances up to $500 Transfer fee: None Central Fidelity Bank: Interest rate: 5% Minimum balance: $500 Monthly fee applied to: Balances up to $500 Transfer fee: None Dominion National Bank: Interest rate: 0 to 5%* Minimum balance: None Monthly fee applied to : Minimum balances up to $500 Transfer fee: None First American: Interest rate: 5 1/4% Minimum balance: $5,000 Monthly fee applied to: Balances up to $2,000 Transfer fee: 50 cents per day Transfer fee applied to: All balances National Bank of Fairfax: Interest rate: 0 to 5 1/4% Minimum balance: None Monthly fee applied: Balances to $500 Transfer fee: None National Bank of Washington: Interest rate: 4 1/2% Minimum balance: $1,500 Monthly fee applied to: All balances Transfer fee: None United Virginia Bank: Interest rate: 0 to 5%* Minimum balance: $500 Monthly fee applied to: Balances up to $500 Transfer fee: None Virginia National Bank: Interest rate: 5 1/4% Minimum balance: None Monthly fee applied to: All balances Transfer fee: 20 cents per day MONTLY FEE: $5 Bank of Maryland: Interest rate: 5 1/4% Minimum balance: $500 Monthly fee applied to: Balances up to $500 Transfer fee: 25 cents Transfer fee applied to: All balance Burke and Herbert: Interest rate: 5 1/4% Minimum balance: None Monthly fee applied to: Balances up to $500 Transfer fee: 25 cents Transfer fee applied to: Balances up to $500 Equitable Trust: Interest rate: 5% Minimum balance: None Monthly fee applied to: Balances up to $3,500 Transfer fee: None Riggs National Bank: Interest rate: 5 1/4% Minimum balance: $500, (checking); $1,000, (savings) Monthly fee applied to: Balances up to $500 Transfer fee: 50 cents Transfer fee applied to: Balances up to $1,00 MONTHLY FEE: $6 Citizens National Bank: Interest rate: 5 1/4% Minimum balance: $1,000 Monthly fee applied to: Balances up to $1,000 Transfer fee: None First Merchants: Interest rate: 5 1/4% Minimum balance: $5,000 Monthly fee applied to: Balances up to $500 Transfer fee: None *Balances up to $500 draw 0% interest; $1,000, 2%; $1,500, 3%; and over $1,500, 5 1/4%.