Give existing clients ninety days of notice, keep their current rate until their package renews, and apply the new rate to new clients immediately.
One client of ours raised her rates by thirty percent this way and lost one client out of fourteen. The client she lost had been asking for discounts for a year.
One of our clients, a solo consultant, lost a retainer that made up forty percent of her income. Her first instinct was to discount everything to fill the gap quickly.
We worked on separating the facts from the story. The fact was a cash-flow gap of three months. The story was that her business was failing. Once the two were apart, she could plan for the gap instead of reacting to the story.
She kept her prices, reached out to five past clients and filled most of the gap within ten weeks. The lesson she took away was to never let one client exceed a quarter of revenue again.