Could somebody advise me on this ? my dog?

as got a little podgey he's an old man and now prefers to just go into the garden rather than for a walk he is on joint tablets ( glucosamine ) and i have now put him on a home diet of fish/chicken/rice and veg which he loves and has lost a couple of pounds on this, how long do you think i could do this for only i feel he could be doing of loosing another 3 or 4lb i don't want to have to pay for vet dietary food when i can make up my own at home and quite cheaply he's been on this since Saturday , what do you think?. Please only sensible answers.