Wales beat Belgium 1-0 to move three points clear at the top of Group B.
With home matches against Israel and Andorra and trips to Cyprus and Bosnia-Hercegovina to come, Toshack thinks Wales can qualify.
"With the points they've got at the moment, I think another four points will see them there," he said.
In an interview with BBC Radio 5 live, Toshack added: "The games in Cyprus and Bosnia will be tricky little games but they have Andorra at home to play."
Wales have 14 points from their six games in Group B, which gives them a three-point lead over second-placed Belgium and a five-point advantage over Israel and Cyprus.
Chris Coleman's men would all but seal their place at Euro 2016 by beating Cyprus and Israel in their September double-header.
If they do so and Bosnia fail to beat Belgium in Brussels, they will be assured of their place in next year's tournament in France.
Wales finish with games away to Bosnia and home to Andorra in October.
Wales have not qualified for a major tournament since the 1958 World Cup, but Friday's win against Belgium has given them a golden opportunity to break that barren spell.
Gareth Bale marked his 50th cap with the winner at Cardiff City Stadium, his 17th goal for his country and his fifth of this qualifying campaign.
The 25-year-old endured a testing second season with Real Madrid, in which he was criticised by fans and media.
But the world's most expensive player has enjoyed a stellar campaign with Wales, where he has revelled in a roaming role behind striker Hal Robson-Kanu.
Toshack, who had two spells in charge of Real Madrid, believes the Spanish side have failed to make full use of Bale's ability.
"Gareth has had a difficult time at Madrid recently," said Toshack, who gave Bale his Wales debut in 2006.
"Playing him wide right I'm not sure is the best position for him.
"They paid an awful lot of money for him at Real Madrid. He's a super player, we know that."
Former manager John Toshack believes four points from four remaining qualifiers will be enough to seal Wales' passage to Euro 2016.