Candidates, get out your No. 2 pencils.

Three of the four Senate candidates in Rhode Island have personal wealth enough to trigger the millionaire’s amendment — the campaign regulation that took effect in the previous cycle allowing candidates of modest means to raise more money from individuals when facing free-spending rich opponents.

But figuring out who will spend enough to cross the threshold, and at what point one’s opponent can begin raising money in $6,000 and $12,000 increments, is a lot more complex.

Former Rhode Island Attorney General Sheldon Whitehouse (D) and Cranston Mayor Stephen Laffey (R) have both contributed $360,000 to their respective campaigns while neither Sen. Lincoln Chafee (R) nor Rhode Island Secretary of State Matt Brown (D) has put in a penny. Brown is the only contender who is not a millionaire.

The law takes into account the voting-age population of individual states, how much candidates raise from outside sources and the stage of the election cycle and plugs it into a convoluted formula.

“You have to be a mathlete,” joked Cleta Mitchell, outside counsel for the National Republican Senatorial Committee.

Nonetheless, it pays to keep abreast of the issue as the Federal Election Commission does not notify campaigns when they can begin collecting additional money. It is up to the self-financing candidate to alert the FEC and his opponents.

At this stage, it appears the candidate who stands to benefit the most is Brown.

Whitehouse need only spend an additional $18,000 and change before Brown can go back to donors who maxed out with $2,000 contributions and ask for as much as $4,000 more.

“We’ll definitely take advantage of that rule,” said Brown spokesman Matt Burgess.

Whitehouse, for his part, is not tipping his hand as to whether Brown will get that opportunity.

“Sheldon Whitehouse is working hard to raise the money he’ll need for a successful campaign,” Whitehouse spokesman Mike Guilfoyle said. “Last quarter he raised more than Brown and Chafee combined and he’s confident that he’ll have the resources necessary to run a winning campaign.”

By not telegraphing their intentions, or by waiting until late in the cycle to infuse their campaign with a lot of personal money, self-funding candidates may have an advantage.

Tripping the trigger out of the gate allows rivals to take full advantage of the provision, one consultant acknowledged.

“Where it’s particularly helpful is when you’re running against someone not only with deep pockets but also who’s building a huge infrastructure so that they spend a lot of money early,” said Pete Giangreco, whose firm, The Strategy Group, handled direct mail and served as general strategists for the successful campaign of Sen. Barack Obama (D-Ill.) last year.

Obama won a crowded primary aided by the additional funds he raised because one opponent, multimillionaire Blair Hull, ultimately spent about $29 million of his own money.

“It’s certainly a lot easier to go back to people who love you and know you and wish they could give more than to find new donors” down the stretch, Giangreco said.

Obama’s success exemplified how the rule is intended to work, but it also might serve as a warning to self-funding candidates everywhere, Giangreco said.

“Where it doesn’t work is when they break [the cap] late,” Giangreco said. “Hull broke it early and I think that’s a bit of lesson for self-funding candidates. They can try to run a lean campaign up front” thereby robbing their opponents of extra time to raise additional funds but then they might not have the money they need, he said. “It’s a Catch-22.”

Someone triggering the millionaire’s amendment is not an automatic boom for his rival’s campaign, Mitchell noted.

“Just because you can raise money in $6,000 and $12,000 increments doesn’t mean there are people waiting to give you more,” she said.

When candidates file their initial FEC paperwork they must indicate how much money above the thresholds they intend to spend on their races.

Mitchell said it is not a binding number but it is intended to give opponents a fair estimation of what to expect.

Mitchell said Laffey was disingenuous when he marked zero on his form, which makes it difficult for Chafee to plan.

“It’s hard to predict that when you have a candidate who is violating, if not the letter, the spirit of the law,” Mitchell said.

Robin Muskian-Schutt, Laffey’s campaign spokeswoman, said neglecting to include a dollar figure on the form was an oversight.

“If there’s an error on that we will of course amend it,” she said.

Whitehouse amended his form to indicate that he would exceed the threshold by $180,000.

The threshold for Rhode Island — which does not trigger additional fundraising — is $183,345, therefore both Laffey and Whitehouse already have exceeded it.

In order for Chafee to collect donations in larger increments, however, Laffey would have to spend about $1 million of his own money.

“His personal investment to this point clearly shows a commitment” to the race, Muskian-Schutt said. Laffey “doesn’t expect to [spend that much] but is leaving his options open.”

Ian Lang, Chafee’s campaign spokesman, said the Senator’s campaign is ready.

“Given the fact that Mr. Laffey said he was not going to exceed the threshold and he already has as well as Sheldon Whitehouse’s history of spending personal money in losing primary races, I think it’s certainly conceivable that it will be triggered” in both primaries, Lang said.

Chafee spent $300,100 of his own money on his 2000 election. As to this race, Chafee has made “no final determination yet,” Lang said. “We’ll continue to review our options.”