The proper way of separating ma’aser-tithes is as follows:

1. At first the person should explicitly make a condition that he is practicing this “without a vow” (b’li neder), so that if he should ever fail to separate ma’aser he will not transgress the sin of Vows [because any good behavior that a person does three times or more is automatically considered a vow]. He should have a special notebook to record all of his earnings (minus expenses), so that he can determine how much needs to be separated as ma’aser.
2. Once in six months, or at least once a year, he should make an accounting of all his earnings. If during that interval he suffered a loss, he should deduct that amount from his total earnings. From the remaining earnings he should separate a tenth for tzedakah.
3. During that same accounting period, he should also record every gift of tzedakah he gives (including even those small coins he gives to the poor who knock at his door). These tzedakah sums are also subtracted from the total he will have to separate.
4. If, at the time of the accounting [at the end of six months or a year], he sees that he has not yet distributed a tenth to tzedakah, then he should immediately separate and distribute the remaining amount to tzedakah. If there are no poor people in his vicinity that need charity just then, he may leave the money in his care in the meantime until poor people come his way. He is even allowed to [temporarily] use that money for his own use, provided that when the poor comes his way, he will borrow the money himself in order to immediately give them the charity money that he had been due to give.

E. If, on the accounting day, he finds that he gave more to tzedakah than the sum of ma’aser he needed to separate — some say that he may subtract that amount from next year’s ma’aser, while other authorities maintain that he is not allowed to do so. Because of this halachic dispute, it is advisable to stipulate from the outset that he may distribute money for tzedakah on condition that he will re-collect [any overpaid sums] from ma’aser funds, whenever they become available [i.e., including from the following year’s income].