I was employed with 401k part year and self-employed the rest of the year. I'm thinking of contributing to SEP-IRA. How much can I contribute?

I took a look at IRS Pub 560 but it was too complex for me to understand. TT Online told me it will guide me through to figure out but it didn't. Do I have to finish all the entries and would TT tell me up to how much I can contribute to SEP-IRA? (This is about 2016 tax. Am I too late?)